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stac-server

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Overview

Stac-server is an implementation of the STAC API specification for searching and serving metadata for geospatial data, including but not limited to satellite imagery). The STAC and STAC API versions supported by a given version of stac-server are shown in the table below. Additional information can be found in the CHANGELOG

stac-server Version(s)STAC VersionSTAC API Foundation Version
0.1.x0.9.x0.9.x
0.2.x<1.0.0-rc.10.9.x
0.3.x1.0.01.0.0-beta.2
0.4.x1.0.01.0.0-beta.5
0.5.x-0.8.x1.0.01.0.0-rc.2
>=1.0.01.0.01.0.0

Currently, stac-server supports the following specifications:

The following APIs are deployed instances of stac-server:

NameSTAC VersionSTAC API VersionDescription
Earth Search v11.0.01.0.0Catalog (v1) of some AWS Public Datasets
USGS Astrogeology STAC API1.0.01.0.0A STAC API for planetary data
Earth Search v01.0.0-beta.20.9.0Catalog (v0) of some AWS Public Datasets
Landsat Look1.0.00.9.0

Architecture

flowchart LR

itemsForIngest[Items for ingest]

subgraph ingest[Ingest]
  ingestSnsTopic[Ingest SNS Topic]
  ingestQueue[Ingest SQS Queue]
  ingestLambda[Ingest Lambda]
  postIngestSnsTopic[Post-Ingest SNS Topic]

  ingestDeadLetterQueue[Ingest Dead Letter Queue]
end

users[Users]

subgraph api[STAC API]
  apiGateway[API Gateway]
  apiLambda[API Lambda]
end

opensearch[(OpenSearch)]

%% Ingest workflow

itemsForIngest --> ingestSnsTopic
ingestSnsTopic --> ingestQueue
ingestQueue --> ingestLambda
ingestQueue --> ingestDeadLetterQueue
ingestLambda --> opensearch
ingestLambda --> postIngestSnsTopic


%% API workflow

users --> api
apiGateway --> apiLambda
apiLambda --> opensearch

Migration

Warnings

3.1.0

OpenSearch Version 2.11

3.0.0

Node 18 update

The default Lambda deployment environment is now Node 18. The major difference between the Node 16 and Node 18 Lambda environment is that the Node 16 env includes AWS SDK for JS v2, and Node 18 includes v3. This code has been updated to use v3, so the Node 18 environment must be used, or the build must be modified to install the v3 libraries.

To update the deployment to use Node 18, modify the serverless config file value provider.runtime to be nodejs18.x and the application re-deployed.

2.4.0

OpenSearch Version 2.9

2.3.0

OpenSearch Version 2.7

0.x or 1.x -> 2.x

Fine-grained Access Control

As of 2.0.0, only OpenSearch is supported and only using fine-grained access control. It is recommended to follow the migration path to upgrade to fine-grained access control first and then upgrade to stac-server 2.x.

Enabling Post-ingest SNS publishing

stac-server now has the ability to publish all ingested entities (Items and Collections) to an SNS topic. Follow these steps to add this to an existing deployment. These configurations are also in the serverless.example.yml file, so reference that if it is unclear exactly where to add this in your config.

The following changes should be added to the serverless.yml file.

Explicitly set the provider/environment setting for STAC_API_URL so the ingested entities published to the topic will have their link hrefs set correctly. If this is not set, the entities will still be published, with with incorrect link hrefs.

STAC_API_URL: "https://some-stac-server.com"

Add the SNS topic resource:

postIngestTopic:
  Type: AWS::SNS::Topic
  Properties:
    TopicName: ${self:service}-${self:provider.stage}-post-ingest

For the ingest Lambda resource definition, configure the ARN to publish to by adding:

environment:
  POST_INGEST_TOPIC_ARN: !Ref postIngestTopic

Add IAM permissions with the statement:

- Effect: Allow
  Action:
    - sns:Publish
  Resource:
    Fn::GetAtt: [postIngestTopic, TopicArn]

0.4.x -> 0.5.x

Elasticsearch to OpenSearch Migration

By default, a new deployment of 0.5.x will use OpenSearch instead of Elasticsearch. There are three options if you have an existing deployment that uses Elasticsearch:

  1. Use stac-server in compatibility mode
    1. Add to serverless.yml environment variables ES_COMPAT_MODE: "true" and retain the existing Elasticsearch 7.10 resource description.
  2. Manage the Elasticsearch/OpenSearch domain outside the stac-server serverless deployment.
    1. With the 0.4.x stac-server code, add DeletionPolicy: Retain to the AWS::Elasticsearch::Domain resource
    2. Deploy the stack to update this property in the deployed CloudFormation Stack.
    3. Remove the AWS::Elasticsearch::Domain resource from serverless.yml, modify all of the variables that were previously dynamically populated by the Elasticsearch resource values to be hard-coded, and re-deploy.
    4. The Elasticsearch domain is now independent of the CF Stack.
    5. With the 0.5.x stac-server code, update the serverless.yml environment variable ES_COMPAT_MODE: "true"
    6. Deploy the 0.5.x stac-server code with the updated serverless.yml file
    7. Through the AWS Console, upgrade the OpenSearch Service domain from Elasticsearch 7.10 to OpenSearch 1.3, retaining the compatibilty mode enabled configuration.
    8. Upgrade the OpenSearch 1.3 domain to OpenSearch 2.5.
    9. Re-deploy the stack without the ES_COMPAT_MODE environment variable set.
  3. (Preferred) Disconnect the Elasticsearch domain from the stac-server CF Stack, deploy a new stac-server CF Stack, upgrade the Elasticsearch domain to OpenSearch, and connect the domain to the new CF Stack. This is described below.

Additionally, the ES_HOST variable used in the serverless.yml file has been renamed OPENSEARCH_HOST.

Preferred Elasticsearch to OpenSearch Migration Process

Note! The migration must be done carefully to avoid losing the database!

The major part of this migration is the use of OpenSearch 2.5 instead of Elasticsearch 7.10. Confusingly, both of these are options in the AWS OpenSearch Service, but the Elasticsearch option is no longer being updated by AWS in favor of OpenSearch.

The migration generally follows the outline in here. The underlying problem being solved here is that the CloudFormation resource AWS::Elasticsearch::Domain is used for Elasticsearch, but AWS::OpenSearchService::Domain is used for OpenSearch, and a CloudFormation update can't "migrate" between these resource types. So, the approach is to upgrade the domain to OpenSearch in compatibility mode, then clone the CloudFormation Stack, and import the OpenSearch domain into it.

  1. With the 0.4.x codebase, change the serverless.yml file to add DeletionPolicy: Retain and UpdateReplacePolicy: Retain to the AWS::Elasticsearch::Domain definition at the same level as the Type and deploy. See instructions for deploying here.
  Type: AWS::Elasticsearch::Domain
  DeletionPolicy: Retain
  UpdateReplacePolicy: Retain
  Properties:
    . . .

  1. The existing Elasticsearch domain must be manually migrated to OpenSearch. Prior to re-deploying the stack, use the AWS Console to manually upgrade the Elasticsearch domain (Actions->Upgrade) to OpenSearch 1.3. Select "Enable compatibility mode" to support the existing stac-server 0.4.x code using the Elasticsearch JavaScript client library (@elastic/elasticsearch version 7.9.0). After this upgrade to OpenSearch 1.3, then upgrade the domain to OpenSearch 2.5.

  2. Create a clone of the stac-server 0.5.x code. Copy and update the serverless.yml file used for the 0.4.0 deployment with these changes:

  1. Run npm run package to generate the CloudFormation templates in the .serverless directory. Extract from the file .serverless/cloudformation-template-update-stack.json a template that only has the OpenSearchInstance resource in it. For example:
{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "A STAC API running on stac-server",
  "Resources": {
    "OpenSearchInstance": {
      "Type": "AWS::OpenSearchService::Domain",
      "DeletionPolicy": "Retain",
      "UpdateReplacePolicy": "Retain",
      "UpdatePolicy": {
        "EnableVersionUpgrade": true
      },
      "Properties": {
        "DomainName": "my-stac-server-dev-es",
        "EBSOptions": {
          "EBSEnabled": true,
          "VolumeType": "gp2",
          "VolumeSize": 35
        },
        "ClusterConfig": {
          "InstanceType": "t3.small.search",
          "InstanceCount": 2,
          "DedicatedMasterEnabled": false,
          "ZoneAwarenessEnabled": true
        },
        "EngineVersion": "OpenSearch_2.3",
        "DomainEndpointOptions": {
          "EnforceHTTPS": true
        }
      }
    }
  }
}

  1. Within CloudFormation, choose Create stack and With existing resources (import resources). Upload the template that contains only the OpenSearch resource. Choose a new stack name for this similar to the old one, e.g., my-stac-server-2-{deploy-stage} and update service name in the serverless.yml file with this name without the deploy stage e.g., my-stac-server-2. When prompted for the name of the OpenSearch Domain, put in the name of the existing one, e.g., my-stac-server-dev-es.

  2. Deploy the new stack with npm run deploy -- --stage {deploy-stage}. This should appear as an update to the CloudFormation stack that was just created manually, and should use the existing OpenSearch domain.

  3. Switch the DNS entry for the domain name to the API Gateway endpoint for the new Stack. See instructions here.

  4. Double-check that the DeletionPolicy: Retain is set on the old Stack for the Elasticsearch/OpenSearch resource, and then delete the old Stack.

Granting Access for Thumbnails

The new experimental endpoint /collections/{c_id}/items/{item_id}/thumbnail will redirect to a URL providing a thumbnail as determined by the assets in an item. If the href for this is an AWS S3 ARN, IAM permissions must be granted for the API Lambda to generate a pre-signed HTTP URL instead. For example:

- Effect: Allow
  Action: s3:GetObject
  Resource: 'arn:aws:s3:::usgs-landsat/*'

0.3.x -> 0.4.x

Create a new deployment, copy the elasticsearch database, and rename indexes.

Elasticsearch upgrade from 7.9 to 7.10

The Serverless Framework supports provisioning AWS resources, but it does not support updating existing resources. In 0.4, the default Elasticsearch version has been updated from 7.9 to 7.10. Continuing to use 7.9 should not cause any problems, but it recommended that you manually upgrade to 7.10 by going to AWS Console - Amazon OpenSearch Service, choosing the Elasticsearch domain used by your stac-server deployment (e.g., stac-server-{stage}-es), choose Upgrade from the Actions menu, and then upgrade to Elasticsearch 7.10.

Disable automatic index creation

It is now recommended to disable automatic index creation.

Validate index mappings

Elasticsearch indices each have a mapping applied that determines how the data is indexed and searched over. These mappings do not change the document data, but can change search behavior. One relevant mapping behavior is that by default, string fields are analyzed for full-text search. In most cases with STAC Items, values such as those in the id and collection fields should not be analyzed and should instead be searchable only by exact matches. In Elasticsearch, this is known as a keyword field type. Importantly, sorting may only be done over keyword typed fields. As of 0.4.0, the default sort is now by properties.datetime, then id, then collection, and results will not be returnd if any indicies have the id or collection fields mapped as text instead of keyword.

For each index (other than collections), use GET to retrieve the endpoint GET /{collectionId}/_mapping, and validate that properties.datetime type is date, and id and collection mappings are keyword (not text with a keyword subfield). For an AWS Opensearch Service instance, this can be done with a script similar to the one here.

The results should look simliar to this:

{
  "my_collection_name": {
    "mappings": {
      "dynamic_templates": [
        ...
        {
          "strings": {
            "match_mapping_type": "string",
            "mapping": {
              "type": "keyword"
            }
          }
        },
        ...
      ],
      "properties": {
        ....
        "id": {
          "type": "keyword"
        },
        "collection": {
          "type": "keyword"
        },
        ....
        "properties": {
          "properties": {
            ...
            "datetime": {
              "type": "date"
            },
            ...
          }
        },
        ...
      }
    }
  }
}

If this is not the case, the easiest solution to fix it is to:

  1. Deploy a 0.4.0 instance.
  2. Backup and restore the 0.3.0 instance's Elasticsearch indicies to the 0.4.0 instances's Elasticsearch database.
  3. Create a collection via ingest with a new collection name similar to the existing one (e.g., if index foo exists, create foo_new).
  4. Reindex from the the existing index (foo) to the the new one (foo_new).
  5. Delete the exiting index and rename the new one to the name of the formerly-existing one (e.g. foo_new -> foo).

Usage

Stac-server is a web API that returns JSON, see the documentation, or the /api endpoint which is a self-documenting OpenAPI document. STAC Index collects information on a number of client tools.

stac-server supports both GET and POST Search requests.

An Item Search with GET:

curl "${HOST}/search?collections=sentinel-2-l2a,sentinel-2-l1c&bbox=10,10,15,15&query=%7B%22eo%3Acloud_cover%22%3A%7B%22gte%22%3A0,%22lte%22%3A5%7D%7D&sortby=-properties.datetime"

Notice that the query parameter is a URL-encoded JSON value.

An Item Search with POST:

curl -X "POST" "${HOST}/search" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{
  "collections": [
    "sentinel-2-l2a",
    "sentinel-2-l1c"
  ],
  "bbox": [
    10,
    10,
    15,
    15
  ],
  "query": {
    "eo:cloud_cover": {
      "gte": 0,
      "lte": 5
    }
  },
  "sortby": {
    "field": "properties.datetime",
    "direction": "desc"
  }
}'

Deployment

This repository contains Node libraries for running the API, along with a serverless configuration file for deployment to AWS.

To create your own deployment of stac-server, first clone the repository:

git clone https://github.com/stac-utils/stac-server.git
cd stac-server

Copy the example serverless config file to a file named serverless.yml:

cp serverless.example.yml serverless.yml

There are some settings that should be reviewed and updated as needeed in the serverless config file, under provider->environment:

NameDescriptionDefault Value
OPENSEARCH_HOSTThe URL of the OpenSearch cluster.
STAC_VERSIONThe STAC version for the STAC objects returned by server. This should not be confused with the STAC API version.1.0.0
STAC_IDID of this catalogstac-server
STAC_TITLETitle of this catalogSTAC API
STAC_DESCRIPTIONDescription of this catalogA STAC API
STAC_DOCS_URLURL to documentationhttps://stac-utils.github.io/stac-server
LOG_LEVELLevel for logging (error, warn, info, http, verbose, debug, silly)warn
REQUEST_LOGGING_ENABLEDExpress request logging enabled. String 'false' disables.enabled
REQUEST_LOGGING_FORMATExpress request logging format to use. Any of the Morgan predefined formats.tiny
STAC_API_URLThe root endpoint of this APIInferred from request
ENABLE_TRANSACTIONS_EXTENSIONBoolean specifying if the Transaction Extension should be activatedfalse
STAC_API_ROOTPATHThe path to append to URLs if this is not deployed at the server root. For example, if the server is deployed without a custom domain name, it will have the stage name (e.g., dev) in the path.""
PRE_HOOKThe name of a Lambda function to be called as the pre-hook.none
POST_HOOKThe name of a Lambda function to be called as the post-hook.none
ES_COMPAT_MODEEnable Elasticsearch 7.10 compatibility mdoe within the server.false
OPENSEARCH_CREDENTIALS_SECRET_IDThe AWS Secrets Manager secret use for the username and password to authenticate to OpenSearch.
OPENSEARCH_USERNAMEThe username to authenticate to OpenSearch when AWS Secrets Manager is not used.
OPENSEARCH_PASSWORDThe password to authenticate to OpenSearch when AWS Secrets Manager is not used.
COLLECTION_TO_INDEX_MAPPINGSA JSON object representing collection id to index name mappings if they do not have the same names.
ITEMS_INDICIES_NUM_OF_SHARDSConfigure the number of shards for the indices that contain Items.none
ITEMS_INDICIES_NUM_OF_REPLICASConfigure the number of replicas for the indices that contain Items.none
CORS_ORIGINConfigure the value to send for the Access-Control-Allow-Origin CORS header. Should be set to the domain name of the UI if Basic Authentication is enable (e.g., https://ui.example.com).*
CORS_CREDENTIALSConfigure whether or not to send the Access-Control-Allow-Credentials CORS header. Header will be sent if set to true.none
CORS_METHODSConfigure whether or not to send the Access-Control-Allow-Methods CORS header. Expects a comma-delimited string, e.g., GET,PUT,POST.GET,HEAD,PUT,PATCH,POST,DELETE
CORS_HEADERSConfigure whether or not to send the Access-Control-Allow-Headers CORS header. Expects a comma-delimited string, e.g., Content-Type,Authorization. If not specified, defaults to reflecting the headers specified in the request’s Access-Control-Request-Headers header.none

Additionally, the credential for OpenSearch must be configured, as decribed in the section Populating and accessing credentials.

After reviewing the settings, build and deploy:

npm install
npm run build
OPENSEARCH_MASTER_USER_PASSWORD='some-password' npm run deploy

This will use the file serverless.yml and create a CloudFormation stack in the us-west-2 region called stac-server-dev.

After the initial deployment, the MasterUserOptions option in the serverless.yml file can be commented out so that OPENSEARCH_MASTER_USER_PASSWORD does not need to be passed at every deployment.

To change the region or the stage name (from dev) provide arguments to the deploy command (note the additional -- in the command, required by npm to provide arguments):

OPENSEARCH_MASTER_USER_PASSWORD='some-password' npm run deploy -- --stage mystage --region eu-central-1

Multiple deployments can be managed with multiple serverless config files and specified to the deploy command with:

npm run deploy -- --config serverless.some-name.yml

Once deployed, there are a few steps to configure OpenSearch.

OpenSearch Configuration

Disable automatic index creation

It is recommended to disable the automatic index creation. This prevents the situation where a group of Items are bulk indexed before the Collection in which they are contained has been created, and an OpenSearch index is created without the appropriate mappings.

This can either be done by calling the /_cluster/settings endpoint directly:

curl -X "PUT" "${HOST}/_cluster/settings" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -u "admin:${OPENSEARCH_MASTER_USER_PASSWORD}" \
     -d '{"persistent": {"action.auto_create_index": "false"}}'

or setting that configuration via the OpenSearch Dashboard.

OpenSearch fine-grained access control

stac-server supports either fine-grained access control or AWS IAM authentication to OpenSearch. This section describes how to configure fine-grained access control.

Warning: Unfortunately, fine-grained access control cannot be enabled on an existing OpenSearch cluster through the serverless deploy, as this is a restriction of CloudFormation which serverless uses. A migration process between the clusters must be performed similar to the Elasticsearch -> OpenSearch migration process.

The AccessPolicies Statement will restrict the OpenSearch instance to only being accessible within AWS. This requires the user creation steps below be either executed from or proxied through an EC2 instance, or that the Access Policy be changed temporarily through the console in the domain's Security configuration to be "Only use fine-grained access control".

The next step is to create the OpenSearch user and role to use for stac-server. This can either be done through the OpenSearch API or Dashboard.

Option 1 - API method

This assumes the master username is admin and creates a user with the name stac_server. Environment variables HOST and OPENSEARCH_MASTER_USER_PASSWORD should be set in the shell environment.

Create the Role:

curl -X "PUT" "${HOST}/_plugins/_security/api/roles/stac_server_role" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -u "admin:${OPENSEARCH_MASTER_USER_PASSWORD}" \
     -d $'{
  "cluster_permissions": [
    "cluster_composite_ops",
    "cluster:monitor/health"
  ],
  "index_permissions": [
    {
      "index_patterns": [
        "*"
      ],
      "allowed_actions": [
        "indices_all"
      ]
    }
  ],
  "tenant_permissions": [
    {
      "tenant_patterns": [
        "global_tenant"
      ],
      "allowed_actions": [
        "kibana_all_read"
      ]
    }
  ]
}'

Create the User:

curl -X "PUT" "${HOST}/_plugins/_security/api/internalusers/stac_server" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -u "admin:${OPENSEARCH_MASTER_USER_PASSWORD}" \
     -d $'{ "password": "xxx" }'

Double-check the response to ensure that the user was actually created!

Map the Role to the User:

curl -X "PUT" "${HOST}/_plugins/_security/api/rolesmapping/stac_server_role" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -u "admin:${OPENSEARCH_MASTER_USER_PASSWORD}"  \
     -d $'{
  "users": [
    "stac_server"
  ]
}'
Option 2 - Dashboard method

Login to the OpenSearch Dashboard with the master username (e.g. admin) and password. From the left sidebar menu, select "Security". Select "Internal users", and then "Create internal user". Create the user with the name stac_server.

Click "Create New Role". Create a new Role with name stac_server_role with:

Note that several of the indices permissions in cluster_composite_ops action group are required to be applyed to the Cluster permissions. Confusingly, the cluster_all action group does not have those permissions in it because they are indices permissions rather than cluster permissions. This is all very confusing! This issue has been filed against the OpenSearch Security Plugin to request improvements to the documentation.

Add the user stac_server as a mapped user to this role.

Populating and accessing credentials

After you've created the users, you'll need to populate the credentials for the user so that stac-server can access them.

The preferred mechanism for populating the OpenSearch credentials to stac-server is to create a secret in AWS Secret Manager that contains the username and password. The recommended name for this Secret corresponds to the stac-server deployment as ${service}-${stage}-opensearch-user-creds, e.g., my-stac-server-dev-opensearch-user-creds.

The Secret type should be "Other type of secret" and have two keys, username and password, with the appropriate values, e.g., stac_server and whatever you set as the password when creating that user.

Add the OPENSEARCH_CREDENTIALS_SECRET_ID variable to the serverless.yml section environment:

OPENSEARCH_CREDENTIALS_SECRET_ID: ${self:service}-${self:provider.stage}-opensearch-user-creds

Add to the IAM Role Statements:

- Effect: Allow
  Resource: arn:aws:secretsmanager:${aws:region}:${aws:accountId}:secret:${self:provider.environment.OPENSEARCH_CREDENTIALS_SECRET_ID}-*
  Action: "secretsmanager:GetSecretValue"

If desired, the resource ARN can be replaced with the exact ARN for the Secret instead of using an ARN ending with *.

Redeploy to reconfigure OpenSearch and populate the authentication configuration. The server should now be using fine-grained access control.

Alternately, instead of using the preferred mechanism of Secrets Manager, the OPENSEARCH_USERNAME and OPENSEARCH_PASSWORD values can be set directly in the environment section:

OPENSEARCH_USERNAME: stac_server
OPENSEARCH_PASSWORD: xxxxxxxxxxx

Setting these as environment variables can also be useful when running stac-server locally.

stac-server is now ready to ingest data!

Create collection index

The collection index must be created, which stores the metadata about each Collection. Invoke the stac-server-<stage>-ingest Lambda function with a payload of:

{
  "create_indices": true
}

This can be done with the AWS CLI Version 2.

aws lambda invoke \
  --function-name stac-server-dev-ingest \
  --cli-binary-format raw-in-base64-out \
  --payload '{ "create_indices": true }' \
  /dev/stdout

Proxying stac-server through CloudFront

The API Gateway URL associated with the deployed stac-server instance may not be the URL that you ultimately wish to expose to your API users. AWS CloudFront can be used to proxy to a more human readable URL. In order to accomplish this:

  1. Create a new CloudFront distribution (or use an existing distribution).
  2. Set the origin to the Gateway API URL (obtain in the stage view of the deployed stac-server). The URL is in the form <##abcde>.execute-api.region.amazonaws.com.
  3. Set the origin path to the deployed stage name prepended with a /, (e.g., /dev or /prod).
  4. Under behaviors, add a new behavior for the desired URL endpoint or subdomain (e.g., /api or /v0.4.0).
  5. Set the 'Origin and origin groups to the URL defined above ('<##abcde>.execute-api.region.amazonaws.com').
  6. Set Viewer to HTTPS only and Allowed HTTP Methods to 'GET, HEAD, OPTIONS, PUT, POST, PATCH, DELETE'.
  7. Set the Cache Policy to a custom policy that forwards query strings. If one simply disables caching, CloudFront strips the query strings.
  8. Optionally, define a LambdaEdge to perform a URL rewrite. This is necessary if your API URL is appended to the root URL (e.g., mydomain.com/api). The Lambda must rewrite the URL to remove the /api. For example:
from re import sub

def lambda_handler(event, context):
    request = event['Records'][0]['cf']['request']
    uri = request["uri"]

    if uri in ["/", "/index.html"]:
        response = {
            "status": 302,
            "statusDescription": "Found",
            "headers": {
                "location": [{
                    "key": "Location",
                    "value": "/api/"
                }]
            }
        }
        return response

    request["uri"] = sub("^/api", "/", uri)
    print(request)
    return request

Locking down transaction endpoints

If you wanted to deploy STAC Server in a way which ensures certain endpoints have restricted access but others don't, you can deploy it into a VPC and add conditions that allow only certain IP addresses to access certain endpoints. Once you deploy STAC Server into a VPC, you can modify the Resource Policy of the API Gateway endpoint that gets deployed to restrict access to certain endpoints. Here is a hypothetical example. Assume that the account into which STAC Server is deployed is numbered 1234-5678-9123, the API ID is ab1c23def, and the region in which it is deployed is us-west-2. You might want to give the general public access to use any GET or POST endpoints with the API such as the "/search" endpoint, but lock down access to the transaction endpoints (see https://github.com/radiantearth/stac-api-spec/tree/master/ogcapi-features/extensions/transaction) to only allow certain IP addresses to access them. These IP addresses can be, for example: 94.61.192.106, 204.176.50.129, and 11.27.65.78. In order to do this, you can impose a condition on the API Gateway that only allows API transactions such as adding, updating, and deleting STAC items from the whitelisted endpoints. For example, here is a Resource Policy containing two statements that allow this to happen:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": "execute-api:Invoke",
            "Resource": [
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/POST/search",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/POST/search/*",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/GET/search/*",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23defi/v1/GET/*"
            ]
        },
        {
            "Effect": "Allow",
            "Principal": "*",
            "Action": "execute-api:Invoke",
            "Resource": [
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/POST/collections/*/items",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/PUT/collections/*/items/*",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/PATCH/collections/*/items/*",
                "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/DELETE/collections/*/items/*"
            ],
            "Condition": {
                "IpAddress": {
                    "aws:sourceIp": [
                        "94.61.192.106",
                        "204.176.50.129",
                        "11.27.65.78"
                    ]
                }
            }
        }
    ]
}

The first statement in the Resource Policy above grants access to STAC API endpoints for use in general operations like searching, and the second statement restricts access to the Transaction endpoints to a set of source IP addresses. According to this policy, POST, PUT, PATCH, and DELETE operations on items within collections are only allowed if the request originates from the IP addresses 94.61.192.106, 204.176.50.129, or 11.27.65.78. The second statement can also be written in another manner, denying access to the Transaction endpoints for all addresses that don’t match a set of source IP addresses. This is shown below.

{
    "Effect": "Deny",
    "Principal": "*",
    "Action": "execute-api:Invoke",
    "Resource": [
        "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/POST/collections/*/items",
        "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/PUT/collections/*/items/*",
        "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/PATCH/collections/*/items/*",
        "arn:aws:execute-api:us-west-2:123456789123:ab1c23def/v1/DELETE/collections/*/items/*"
    ],
    "Condition": {
        "NotIpAddress": {
            "aws:sourceIp": [
                "94.61.192.106",
                "204.176.50.129",
                "11.27.65.78"
            ]
        }
    }
}

AWS WAF Rule Conflicts

Frequently, stac-server is deployed with AWS WAF protection. When making a POST request that only has the limit parameter in the body, a WAF SQL injection protection rule incurs a false positive and returns a Forbidden status code. This request is an example:

curl -X POST ${HOST}/search -d '{"limit": 1}'

This is also triggered when using pystac_client with no filtering parameters.

The fix is to disable the WAF SQL injection rule, which is unnecessary because stac-server does not use SQL.

API Gateway Logging

The example serverless.yml config contains disabled configuration for setting up API Gateway logging of API requests. More information about these configuration can be found in the Serverless Framework API Gateway Documentation.

The executionLogging setting causes logging of the actual execution of the API Gateway endpoints and backing Lambda, with fullExecutionData causing the entire request and response to be logged to CloudWatch, which can be expensive.

The accessLogging setting logs the values specified in format to CloudWatch, which can be useful for computing metrics on usage for the API.

Queryables

STAC API supports the Query Extension. Unlike the Filter Extension (which is not supported), the Query Extension does not (yet) define a mechanism to advertise which terms may be used in expressions. However, an optional defintion may be added to it soon that defines queryables endpoints the same as used with Filter Extension. To define these for a Collection, add a field queryables with the value as the JSON Schema definition of the queryables for that collection. This will be used for a collection's queryables resource, and removed from the Collection entity whenever that is returned.

A non-configurable root-level queryables definition is defined with no named terms but additionalProperties set to true.

Aggregation

STAC API supports the Aggregation Extension. This allows the definition of per-collection aggregations that can be calculated, dependent on the relevant fields being available in the STAC Items in that Collection. A field named aggregations should be added to the Collection object for the collection for which the aggregations are available, e.g.:

  "aggregations": [
    {
      "name": "total_count",
      "data_type": "integer"
    },
    {
      "name": "datetime_max",
      "data_type": "datetime"
    },
    {
      "name": "datetime_min",
      "data_type": "datetime"
    },
    {
      "name": "datetime_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "datetime"
    },
    {
      "name": "grid_code_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    },
    {
      "name": "centroid_geohash_grid_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    },
    {
      "name": "centroid_geohex_grid_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    },
    {
      "name": "centroid_geotile_grid_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    },
      {
      "name": "geometry_geohash_grid_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    },
    {
      "name": "geometry_geotile_grid_frequency",
      "data_type": "frequency_distribution",
      "frequency_distribution_data_type": "string"
    }
  ]

Available aggregations are:

Ingesting Data

STAC Collections and Items are ingested by the ingest Lambda function, however this Lambda is not invoked directly by a user, it consumes records from the stac-server-<stage>-queue SQS. To add STAC Items or Collections to the queue, publish them to the SNS Topic stac-server-<stage>-ingest.

STAC Collections must be ingested before Items that belong to that Collection. Items should have the collection field populated with the ID of an existing Collection. If an Item is ingested before ingestion of the Collection it contains, ingestion will either fail (in the case of a single Item ingest) or if auto-creation of indexes is enabled (default) and multiple Items are ingested in bulk, the auto-created index will have incorrect mappings.

If a collection or item is ingested, and an item with that id already exists in STAC, the new item will completely replace the old item.

After a collection or item is ingested, the status of the ingest (success or failure) along with details of the collection or item are sent to a post-ingest SNS topic. To take action on items after they are ingested subscribe an endpoint to this topic.

Messages published to the post-ingest SNS topic include the following atributes that can be used for filtering:

attributetypevalues
recordTypeStringCollection or Item
ingestStatusStringsuccessful or failed
collectionString

Ingesting large items

There is a 256 KB limit on the size of SQS messages. Larger items can by publishing a message to the stac-server-<stage>-ingest SNS topic in with the format:

{
  "href": "s3://source-bucket/source-key"
}

The s3://, http://, and https:// protocols are supported for remote ingest.

Subscribing to SNS Topics

Stac-server can also be subscribed to SNS Topics that publish complete STAC Items as their message. This provides a way to keep stac-server up to date with new data. Use the AWS Lambda console for the function stac-server-<stage>-subscibe-to-sns to subscribe to an SNS Topic for which you have the full ARN and permission to subscribe to. This could be an SNS Topic you created yourself to publish STAC records to, or a publicly available one, such as for Sentinel.

Note, that adding the subscription via the topic page does not seem to work. Instead, add a trigger on Lambda edit page.

Ingest Errors

Errors that occur while consuming items from the ingest queue will end up in the dead letter processing queue.

Supporting Cross-cluster Search and Replication

OpenSearch support cross-cluster connections that can be configured to either allow search across the clusters, treating a remote cluster as if it were another group of nodes in the cluster, or configure indicies to be replicated (continuously copied) from from one cluster to another.

Configuring either cross-cluster behavior requires fine-grained access control.

Cross-cluster Search

The AWS documentation for cross-cluster search can be found here.

  1. Ensure fine-grained access control is enabled.
  2. Create a connection between the source and destination OpenSearch domains.
  3. Ensure there is a es:ESCrossClusterGet action in the destination's access policy.
  4. In the source stac-server, create a Collection for each collection to be mapped. This must have the same id as the destination collection.
  5. For the source stac-server, configure a COLLECTION_TO_INDEX_MAPPINGS environment variable with a stringified JSON object mapping the collection name to the name of the index. For example, {"collection1": "cluster2:collection1", "collection2": "cluster2:collection2"} is a value mapping two collections through a connection named cluster2. Deploy this change.

Cross-cluster Replication

The AWS documentation for cross-cluster replication can be found here.

  1. Ensure fine-grained access control is enabled (default as of v2.0.0)
  2. Create the replication connection in the source to the destination
  3. Create the collection in the source's stac-server instance

Pre- and Post-Hooks

Stac-server supports two hooks into the request process: a pre-hook and a post-hook. These are each Lambda functions which, if configured, will be invoked by stac-server. It is assumed that the stac-server Lambda has been granted permission to invoke these Lambda functions, if configured.

Pre-Hook

If the stac-server is deployed with the PRE_HOOK environment variable set to the name of a Lambda function, then that function will be called as the pre-hook.

The event passed into the pre-hook Lambda will be an instance of an API Gateway Proxy Event.

If the return value from the pre-hook Lambda is an instance of an API Gateway Proxy Result, then that response will immediately be returned to the client.

If the return value of the pre-hook Lambda is an instance of an API Gateway Proxy Event, then that event will be passed along to stac-server.

If the pre-hook Lambda throws an exception, an internal server error will be returned to the client.

The pre-hook Lambda configuration may reference any Lambda, not only one deployed as part of this stack. There is an example pre-hook Lambda that can be included with this stack, which provides an example rudimentary authorization mechanism via a hard-coded token.

To enable this example pre-hook:

Post-Hook

If the stac-server is deployed with the POST_HOOK environment variable set to the name of a Lambda function, then that function will be called as the post-hook.

The event passed into the post-hook labmda will be the response from the stac-server, and will be an instance of an API Gateway Proxy Result.

The return value of the post-hook Lambda must be an instance of an API Gateway Proxy Result.

If the post-hook Lambda throws an exception, an internal server error will be returned to the client.

The post-hook Lambda configuration may reference any Lambda, not only one deployed as part of this stack. There is an example post-hook Lambda that can be included with this stack, which does nothing, but shows how the API Lambda response can be modified.

The post-hook Lambda configuration may reference any Lambda, not only one deployed as part of this stack. There is an example post-hook Lambda that can be included with this stack, which provides an example of how to interact with the response, but does not modify it.

To enable this example post-hook:

Request Flow

flowchart
  client -- APIGatewayProxyEvent --> pre-hook
  pre-hook[pre-hook Lambda]
  pre-hook -- APIGatewayProxyResult --> client
  pre-hook -- APIGatewayProxyEvent --> stac-server
  post-hook[post-hook Lambda]
  stac-server -- APIGatewayProxyResult --> post-hook
  post-hook -- APIGatewayProxyResult --> client

Notes

Lambda payloads and responses must be less than 6 MB. A larger payload will result in an internal server error being returned to the client.

The outputs of the pre- and post-hooks are validated and, if they don't comply with the defined schemas, an internal server error will be returned to the client. Information about the invalid event, as well as details about the parsing errors, will be logged to CloudWatch.

Development

Install NVM to manage your Node.js environment.

# uses version in .nvmrc
nvm install
nvm use

The package-lock.json was built with npm 8.5.0, so use at least this version.

There are several useful npm commands available to use locally:

# Install dependencies in package.json
npm install

# Run the build command in each of the packages (runs webpack)
npm run build

# Run ESLint
npm run lint

# To run tests for all packages
npm run test

# To build API docs from the api spec
npm run build-api-docs # TODO: this fails

Running Locally

Before the API can be run, OpenSearch and Localstack need to be running. There is a docker-compose.yml file to simplify running OpenSearch locally:

docker-compose up -d

The API can then be run with:

npm run serve

Connect to the server on http://localhost:3000/

Other configurations can be passed as shell environment variables, e.g.,

export ENABLE_TRANSACTIONS_EXTENSION=true
export OPENSEARCH_HOST='https://search-stac-server-dev-7awl6h344qlpvly.us-west-2.es.amazonaws.com'
npm run serve

Running Unit Tests

stac-server uses ava to execute tests.

# alias to run unit tests
npm test

# run unit tests in tests directory
npm run test:unit

# run unit tests with coverage
npm run test:coverage

# run tests from a single test file whose titles match 'foobar*'
npx ava tests/test-es.js --match='foobar*'

Running System and Integration Tests

The System and Integration tests use an OpenSearch server running in Docker and a local instance of the API.

When the system tests run, they:

  1. Wait for OpenSearch to be available
  2. Delete all indices from OpenSearch
  3. Start an instance of the API. That API will be available at http://localhost:3000/dev/
  4. Wait for the API to be available
  5. Run the system tests in ./tests/system/test-*.js
  6. Stop the API

Before running the system tests, make sure to start OpenSearch using:

docker-compose up -d

Running these tests requires the timeout utility is installed. On Linux, this is probably already installed, and on macOS it can be installed with brew install coreutils.

Once OpenSearch has been started, run the system tests:

npm run test:system

A subset of system tests may be run by providing a glob matching the test files to run:

npm run test:system test-api-item-*

Run the integration tests (Note: currently none exist):

npm run test:integration

Updating the OpenAPI specification

The OpenAPI specification is served by the endpoint /api.

This file is location in src/lambdas/api/openapi.yaml.

When the API is updated to a new STAC API release, this file must be updated. To update it, first install yq, then run:

bin/build-openapi.sh

This script combines all of the STAC API OpenAPI definitions for each conformance class into one file.

Next, edit that file to make it specific to this server. For example:

To validate the resulting OpenAPI file, run

npm run check-openapi

and fix any errors or warnings.

About

stac-server was forked from sat-api. Stac-server is for STAC versions 0.9.0+, while sat-api exists for versions of STAC prior to 0.9.0.

License

stac-server is licensed under The MIT License. Copyright for portions of stac-server is held by Development Seed (2016) as part of project sat-api original license. Copyright for all changes to stac-server since the fork date is held by Element 84, Inc (2020).