Filters

For an overview and basic explanation, visit the filters section in the operators guide.

Filters can be either added by implementing one of the various filter interfaces like HttpInboundSyncFilter in the proxy servers main code or by adding a groovy file in one of the filter directories in the proxy installation folder. Following is a sample implementation of an endpoint Healthcheck filter and inbound Routes filter in groovy. The Routes filter will intercept all requests which have healthcheck in their path and redirect them to the respective endpoint.

Note

Even when writing groovy filters the package declaration is mandatory. Otherwise the dynamic filter activation / deactivation via application.properties will not work as expected.

Endpoint filter:

package groovy.filters.endpoint

class Healthcheck extends HttpSyncEndpoint {

  @Override
  HttpResponseMessage apply(HttpRequestMessage request) {
      HttpResponseMessage resp = new HttpResponseMessageImpl(request.getContext(), request, 200)
      resp.setBodyAsText("healthy")

      // need to set this manually since we are not going through the ProxyEndpoint
      StatusCategoryUtils.setStatusCategory(request.getContext(), ZuulStatusCategory.SUCCESS)

      return resp
  }
}

Routes filter:

package groovy.filters.inbound

class Routes extends HttpInboundSyncFilter {

  @Override
  int filterOrder() {
      return 0
  }

  @Override
  boolean shouldFilter(HttpRequestMessage httpRequestMessage) {
      return true
  }

  @Override
  HttpRequestMessage apply(HttpRequestMessage request) {
      SessionContext context = request.getContext()
      String path = request.getPath()
      String host = request.getOriginalHost()

      // Route healthchecks to the healthcheck endpoint.;
      if (path.equalsIgnoreCase("/healthcheck")) {
          context.setEndpoint(Healthcheck.class.getCanonicalName())
      }
      else {
          context.setEndpoint(ZuulEndPointRunner.PROXY_ENDPOINT_FILTER_NAME);
          context.setRouteVIP("api")
      }

      return request
  }
}

filterOrder()

This orders all loaded filters of a type. Lowest numbers will be executed first.

shouldFilter()

Which preconditions have to be met, for this filter to be executed.

apply

What should be done in this filter

Note

The Context object, that is used in the Routes example, is a crucial component of the filter framework used by zuul. With it, the developer can easily transfer data between a filter and its descendants. Each Context is unique to every request.

For more information about filters, please take a look at the example filters in the Zuul 2 repository, found here .