feat(backend): init horizontal clustering

[lusergit]

Horizontally clustering edgheog

Based on #1199

These changes aim at automatically scale edgheog when multiple nodes are able to see each other.

libcluster

libcluster is being added to allow different nodes to see each other. Depending on the deployment environment, different strategies can be selected to query services and discover other edgheog instances in the same cluster.

horde

Horde has been added to allow registries with different processes to share the load across multiple replicas. This would allow a better management of active processes and automatically handles netsplits.

Checklist

• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added or updated documentation (if appropriate)

Further Comments

Communication between different services of edgehog happen trough the pubsub module (Edgehog.PubSub), which internally uses the Phoenix.PubSub. This mechanism already shares messages between different replicas, hence messages are free to pass between one replica and the other
(e.g., a campaign is started on one node, hence its process is active on one node, but a deployment is updated in another node. In this case the pubsub mechanism correctly messages all listening services, even the one on different nodes, and the services should be able to work as usual).

Optional: testing

Testing this new feature can be done by adding

  edgehog-backend:
    image: edgehogdevicemanager/edgehog-backend:0.10.0
    build:
      context: backend
    # This section here
    deploy:
      replicas: 6 
    # ...

In the docker-compose.yaml file

[coveralls]

Pull Request Test Coverage Report for Build 0f8a90b75d89dc74710f86829858fc0614fd290a-PR-1201

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 24 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.3%) to 81.35%

---

Files with Coverage Reduction	New Missed Lines	%
lib/edgehog/application.ex	1	88.89%
lib/edgehog/devices/reconciler/reconciler.ex	7	31.82%
lib/edgehog/config.ex	16	41.18%

Totals
Change from base Build 898ad56e5c2bac7413e1fdf031b5c9c6243cad6a:	-0.3%
Covered Lines:	2735
Relevant Lines:	3362

---

💛 - Coveralls