Middlewares¶

Blacksmith middleware can be configured using the configurator.

Loading middlewares¶

The list of middleware are defined under the setting key blacksmith.client.middlewares, as in the example above.

blacksmith.client.middlewares =
   prometheus

Then each middleware should be configured under the key blacksmith.client.middleware.<name> such as blacksmith.client.middleware.prometheus in the previous example.

To load a custom middleware, a class can be passed on the same line

blacksmith.client.middlewares =
   mybuilder  my.own.module:MyMiddlewareBuilder

In the example above, the class MyMiddlewareBuilder overrides the class pyramid_blacksmith.AbstractMiddleware.

Prometheus Middleware¶

# Optional configuration for the buckets
blacksmith.prometheus_buckets =
    buckets            0.05  0.1  0.2  0.4  1.6  3.2  6.4 12.8 25.6
    hit_cache_buckets 0.005 0.01 0.02 0.04 0.16 0.32 0.64 1.28 2.56

blacksmith.client.middlewares =
   prometheus

Note

The hit_cache_buckets setting is used by the HTTP Cache Middleware.

The prometheus middleware alone is only used to track metrics HTTP queries.

Circuit Breaker Middleware¶

blacksmith.client.middlewares =
   circuitbreaker

# Optional configurations
blacksmith.client.middleware.circuitbreaker =
   threshold   7
   ttl         42

The threshold is the maximum number of consecutive failure to attempt before opening the circuit. The ttl is the number of second the circuit stay open.

Note

Blacksmith circuit breaker is based on purgatory.

Read the purgatory documentation for more information.

Collect Circuit Breaker in prometheus¶

To properly works together, middleware must be added in this order:

blacksmith.client.middlewares =
   prometheus
   circuitbreaker

Using redis as a storage backend¶

blacksmith.client.middlewares =
   circuitbreaker

blacksmith.client.middleware.circuitbreaker =
   uow   purgatory:SyncRedisUnitOfWork

blacksmith.client.middleware.circuitbreaker.uow =
   url   redis://host.example.net/42

HTTP Cache Middleware¶

blacksmith.client.middlewares =
   http_cache

blacksmith.client.middleware.http_cache =
   redis       redis://foo.localhost/0

To override the policy, or the serializal some additional configuration keys are avaiable:

 blacksmith.client.middleware.http_cache =
      redis       redis://foo.localhost/0
      policy      path.to.module:SpecificCachePolicy
      serializer  path.to.module:SpecificSerializer

blacksmith.client.middleware.http_cache.policy =
   key val
   key2 val2

In that case, the class SpecificCachePolicy has been created in the path.to.module and implement the AbscractCachePolicy of blacksmith. The contructor accept parameter key and key2. Note that, to keep the configuration readable, those parameters must be of type str.

By default, the serializer is using json. The key serializer path.to.module:SpecificSerializer. The AbstractSerializer of blacksmith must be implemented.

HTTP Static Headers Middleware¶

Inject a header in every requests the client is consuming. This may be userfull for a client that consume an api using an apikey

blacksmith.client.middlewares =
   static_headers

blacksmith.client.middleware.static_headers =
   Authorization: Apikey xyz
   My-Customer-Header: whatever