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Adopting Erlang service discovery project
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README.md

service_discovery

This project contains applications for creating and updating services over HTTP and grpc that can be queried through DNS. The provided backing storage is through Postgres.

Disclaimer: The purpose of creating this project was the need Adopting Erlang had for a "real-world-esque" project to show the development and production patterns, structure and workflow we use. However, some decisions are made for the purpose of demonstration only, and not because we sat down and determined a certain strategy was optimal for some use case. The use of Postgres as the default storage backend is an example of this. This doesn't mean Postgres isn't a perfectly valid solution for a service discovery backend, and for many use cases even an optimal backend. The point is that it was chosen so that working with Postgres connections, queries and migrations from Erlang could be covered.

Running Locally

A Postgres instance can be started and have the migrations in the directory sql/ run on it with docker-compose:

$ docker-compose up

This will bring up the database and run the migrations in the foreground, you can use -d to start them in the background.

With the database running the service_discovery applications can be started and drop you into a shell with:

$ rebar3 shell

This will be running an HTTP interface on port 3000 and grpc on 8081. The following curl commands will add a service named webapp with a single endpoint 127.0.0.1 and port named http with value 8000 :

$ curl -v -XPUT http://localhost:3000/service -d '{"name": "webapp", "attributes": {"attr-1": "value-1"}}'
$ curl -v -XPUT http://localhost:3000/service/webapp/register -d '{"ip": "127.0.0.1", "tags": []}'
$ curl -v -XPUT http://localhost:3000/service/webapp/port -d '{"http": {"protocol": "tcp", "port": 8000}}'

service_discovery will also be running a DNS server on port 8053 and after adding the endpoint and port it can be queried with dig for the new service webapp:

$ dig -p8053 @127.0.0.1 _http._tcp.webapp.svc.cluster.local SRV
...
_http._tcp.webapp.svc.cluster.local. 3600 IN SRV 1 1 8000 webapp.svc.cluster.local.
...
$ dig -p8053 @127.0.0.1 webapp.svc.cluster.local A
...
webapp.svc.cluster.local. 3600 IN	A	127.0.0.1
...

Running in Kubernetes Locally

$ microk8s.enable registry
$ microk8s.enable dns

=/etc/docker/daemon.json=

{
  ...
  "insecure-registries" : ["localhost:32000"]
  ...
}
$ tilt up
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