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Rails microservices example

This repo contains a very simple example of how you can communicate microservices running inside containers in different nodes inside of a CoreOS cluster. This can be a good starting point for developing distributed rails microservices using docker and CoreOS.

The two services are very simple. Just two models: user and comment. The idea it's to launch two separate containers in different nodes of a cluster and allow communication between the services using http calls.

Once you have the project setted up, you'll have a /user/1/comments url, which will be pointing to one service, but fetching the data from another service.

Instructions

First you need your own discovery URL in order to manage your CoreOS cluster. In this example we are going to use 3 nodes, so first get a valid token using:

curl https://discovery.etcd.io/new?size=3

Put that in the user-data config file replacing the discovery field.

Next, run:

vagrant up

Vagrant is going to bring three CoreOS nodes already configured to works as a cluster.

Login into the first node using the following commands: More info about this here.

ssh-add ~/.vagrant.d/insecure_private_key
vagrant ssh core-01 -- -A

Now that you are inside of the node 01, go to the share folder (shared with the host) and you'll see the two services folders (user and comment). In each one of this folders you're going to find rails applications and systemd services for running the containers inside the cluster.

First, go inside the comment-service folder and run:

fleetctl load comment.service
fleetctl load commentsk.service

The comment.service service is going to create and run the container with the first Rails application. The second is just a sidekick for getting information about the first containers host, since the other microservice has to communicate with it, and we don't know in which one of the three nodes is going to be deployed. More info about this here.

Now that the services are loaded, you can run:

fleetctl start comment.service
fleetctl start commentsk.service

Fleetctl is going to run the first microservice somewhere in the cluster. The first time is going to take more time, since docker needs to build the rails application container. You can follow the container log using journal:

fleetctl journal -f comment.service

With journal you can tail the log of the container, no matter in which host is running.

Once it's finished you should see Webrick running in the port 3000 of the container. The configuration forwards the 3000 port to the 3001 port on the host machine.

In order to see the host in which the service is running, execute:

fleetctl list-units

list-units is going to show you all the units in the cluster and the ip of the host in which the container is running.

For example, if list-units gives you something like this:

UNIT			MACHINE				ACTIVE	SUB
comment.service		5503faa2.../172.17.8.102	active	running
commentsk.service	5503faa2.../172.17.8.102	active	running

it means that the comment service is running in

http://172.17.8.102:3001/comments

So if you visit this url, you'll see the results from the first rails application.

Now that we have the first service running, go to the user-service folder and run the user.service:

fleetctl load user.service
fleetctl start user.service

Fleetctl again is going to deploy the container in one of the nodes of the cluster. Probably a different one this time. Follow the container's log using journal:

fleetctl journal -f user.service

Once docker finishes, check for the host of the user service:

fleetctl list-units


UNIT			MACHINE				ACTIVE	SUB
comment.service		5503faa2.../172.17.8.102	active	running
commentsk.service	5503faa2.../172.17.8.102	active	running
user.service		84eb6850.../172.17.8.103	active	running

In my case, the user service is running in the third node with the address:

http://172.17.8.103:3000/users

This data is from the user service, but if you visit

/users/1/comments

You'll see the comments for the first user but fetched from the other service and from another host probably. All this data is being fetched from sqlite in case you wonder.

Relevant files

To save you some time, the relevant files are:

Rails comments service controller

Rails user service controller

Rails user service model

systemd comment service for fleet

systemd comment service sidekick for fleet

systemd user service for fleet

TODO

More info

If you are interested in this project or you have doubts about setting it up, just create an issue or a pull request.