Rate limiter backend backed by a Hammer rate limiter module.

This is the supported route to cluster-wide rate limiting: point it at a Hammer module using a shared backend (such as hammer_backend_redis) and every node in the cluster meters against the same counters, so the external service sees the limit you configured rather than that limit multiplied by your node count.

Define and supervise a Hammer module as Hammer documents:

defmodule MyApp.RateLimit do
  use Hammer, backend: Hammer.Redis
end

children = [{MyApp.RateLimit, url: "redis://localhost:6379"}]

Then point a service at it:

use ExternalService,
  rate_limit: [
    limit: 100,
    per: :timer.seconds(1),
    backend: {ExternalService.RateLimiter.Hammer, module: MyApp.RateLimit}
  ]

Options

• :module (required) - the Hammer rate limiter module to meter against.
• :key - the Hammer key to meter under. Defaults to a key derived from the service name. Set this explicitly when several services (or several applications) should share one budget.

:hammer is not a dependency of this library. The backend calls hit/3 on the module you supply, which is Hammer's own API, so nothing needs to be added to your dependencies beyond Hammer itself.