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ProxyInterface.md

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Gremlin is agnostic of the service proxy implementation. It only requires the proxy to be capable of injecting the three basic types of faults into API calls between microservices.

There are several ways in which you could implement a service proxy. Some well known approaches include sidecar-based solutions such as Nginx managed by Confd, Ambassador containers in Kubernetes, AirBnB SmartStack, Netflix Prana, library-based options such asNetflix Ribbon, or API gateway patterns such as Mashape's Kong, and cloud-hosted solutions such as IBM Service Proxy.

The only requirement for Gremlin is that the service proxy should support fault injection, and should be programmable over a REST API. A reference implementation of a service proxy with fault injection support can be found at gremlinproxy.

  • For fault injection, a service proxy implementation needs to support 3 key primitives: abort, delay, and mangle.

  • Any fault injection rule comprises of a set of regexes that match a request/response, and a combination of one or more of the failure primitives.

  • A service proxy should be able to receive the fault injection rules via a REST API and inject faults on requests matching the rule.

  • A failure scenario is comprised of a set of fault injection rules distributed across one or more service proxies that sit in front of microservices.

The REST APIs that need to be implemented by any type of service proxy are given below.

POST /gremlin/v1/rules/add: add a Rule. Rule will be posted as a JSON. Format is as follows

{
  source: <source service name>,
  dest: <destination service name>,
  messagetype: <request|response|publish|subscribe|stream>
  headerpattern: <regex to match against the value of the X-Gremlin-ID trackingheader present in HTTP headers>
  bodypattern: <regex to match against HTTP message body>
  delayprobability: <float, 0.0 to 1.0>
  delaydistribution: <uniform|exponential|normal> probability distribution function

  mangleprobability: <float, 0.0 to 1.0>
  mangledistribution: <uniform|exponential|normal> probability distribution function

  abortprobability: <float, 0.0 to 1.0>
  abortdistribution: <uniform|exponential|normal> probability distribution function

  delaytime: <string> latency to inject into requests <string, e.g., "10ms", "1s", "5m", "3h", "1s500ms">
  errorcode: <Number> HTTP error code or -1 to reset TCP connection
  searchstring: <string> string to replace when Mangle is enabled
  replacestring: <string> string to replace with for Mangle fault
}

POST /gremlin/v1/rules/remove : remove the rule specified in the message body (see rule format above)

DELETE /gremlin/v1/rules: clear all rules