Question 1

How to set up Discovery with an existing Elixir application?

Accepted Answer

Add Discovery as a dependency in mix.exs, install a Consul agent, define a service with TTL in Consul, and supervise a Discovery.Heartbeat process. Follow the README's steps for publishing status and polling services to enable automatic node connections.

Question 2

What's the difference between Discovery and libcluster for Elixir clustering?

Accepted Answer

Discovery is specifically built around Consul for service discovery and automatic node linking, while libcluster offers more flexible strategies like Kubernetes or DNS-based discovery without Consul dependency. Choose Discovery if you're already using Consul; otherwise, libcluster might be more versatile.

Question 3

Can Discovery work without Consul or with other service registries?

Accepted Answer

No, Discovery is tightly integrated with Consul and requires it for service registration, health checks, and polling. The README does not mention support for alternative registries, so you'd need to use Consul or consider other tools.

Question 4

How to add custom logic when a service becomes available in Discovery?

Accepted Answer

Implement a custom handler by creating a module with Discovery.Handler.Behaviour or pass an anonymous function to Discovery.Poller. For example, use Discovery.Handler.Generic with a function to execute custom code upon service updates, as shown in the handler examples.

Question 5

What are the performance impacts of Discovery's polling mechanism?

Accepted Answer

Polling Consul at configurable intervals can introduce latency in detecting service changes and may not handle rapid updates well. For high-throughput systems, consider tuning the TTL and polling rates, but it may still lag behind event-driven approaches.

Question 6

How to configure consistent hashing for load balancing with Discovery?

Accepted Answer

Use Discovery.select/3 with a hash value to consistently map requests to nodes, or :random for random selection. The README provides examples for implementing this in your application logic, ensuring even distribution across discovered nodes.

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