Envoy Filter

EnvoyFilter provides a mechanism to customize the Envoy configuration generated by Istio Pilot. Use EnvoyFilter to modify values for certain fields, add specific filters, or even add entirely new listeners, clusters, etc. This feature must be used with care, as incorrect configurations could potentially destabilize the entire mesh. Unlike other Istio networking objects, EnvoyFilters are additively applied. Any number of EnvoyFilters can exist for a given workload in a specific namespace. The order of application of these EnvoyFilters is as follows: all EnvoyFilters in the config root namespace, followed by all matching EnvoyFilters in the workload’s namespace.

NOTE 1: Some aspects of this API is deeply tied to the internal implementation in Istio networking subsystem as well as Envoy’s XDS API. While the EnvoyFilter API by itself will maintain backward compatibility, any envoy configuration provided through this mechanism should be carefully monitored across Istio proxy version upgrades, to ensure that deprecated fields are removed and replaced appropriately.

NOTE 2: When multiple EnvoyFilters are bound to the same workload in a given namespace, all patches will be processed sequentially in order of creation time. The behavior is undefined if multiple EnvoyFilter configurations conflict with each other.

NOTE 3: To apply an EnvoyFilter resource to all workloads (sidecars and gateways) in the system, define the resource in the config root namespace, without a workloadSelector.

The example below declares a global default EnvoyFilter resource in the root namespace called istio-config, that adds a custom protocol filter on all sidecars in the system, for outbound port 9307. The filter should be added before the terminating tcp_proxy filter to take effect. In addition, it sets a 30s idle timeout for all HTTP connections in both gateways and sidecars.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: custom-protocol
  namespace: istio-config # as defined in meshConfig resource.
spec:
  configPatches:
  - applyTo: NETWORK_FILTER
    match:
      context: SIDECAR_OUTBOUND # will match outbound listeners in all sidecars
      listener:
        portNumber: 9307
        filterChain:
          filter:
            name: "envoy.filters.network.tcp_proxy"
    patch:
      operation: INSERT_BEFORE
      value:
        # This is the full filter config including the name and config or typed_config section.
        name: "envoy.config.filter.network.custom_protocol"
        config:
         ...
  - applyTo: NETWORK_FILTER # http connection manager is a filter in Envoy
    match:
      # context omitted so that this applies to both sidecars and gateways
      listener:
        filterChain:
          filter:
            name: "envoy.filters.network.http_connection_manager"
    patch:
      operation: MERGE
      value:
        name: "envoy.filters.network.http_connection_manager"
        typed_config:
          "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager"
          common_http_protocol_options:
            idle_timeout: 30s

The following example enables Envoy’s Lua filter for all inbound HTTP calls arriving at service port 8080 of the reviews service pod with labels “app: reviews”, in the bookinfo namespace. The lua filter calls out to an external service internal.org.net:8888 that requires a special cluster definition in envoy. The cluster is also added to the sidecar as part of this configuration.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: reviews-lua
  namespace: bookinfo
spec:
  workloadSelector:
    labels:
      app: reviews
  configPatches:
    # The first patch adds the lua filter to the listener/http connection manager
  - applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
      listener:
        portNumber: 8080
    patch:
      operation: ADD
      filterClass: AUTHZ # This filter will run *after* the Istio authz filter.
      value: # lua filter specification
        name: envoy.filters.http.lua
        typed_config:
          "@type": "type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua"
          inlineCode: |
           function envoy_on_request(request_handle)
             -- Make an HTTP call to an upstream host with the following headers, body, and timeout.
             local headers, body = request_handle:httpCall(
              "lua_cluster",
              {
               [":method"] = "POST",
               [":path"] = "/acl",
               [":authority"] = "internal.org.net"
              },
             "authorize call",
             5000)
           end
  # The second patch adds the cluster that is referenced by the lua code
  # cds match is omitted as a new cluster is being added
  - applyTo: CLUSTER
    match:
      context: SIDECAR_OUTBOUND
    patch:
      operation: ADD
      value: # cluster specification
        name: "lua_cluster"
        type: STRICT_DNS
        connect_timeout: 0.5s
        lb_policy: ROUND_ROBIN
        hosts:
        - socket_address:
            protocol: TCP
            address: "internal.org.net"
            port_value: 8888

The following example overwrites certain fields (HTTP idle timeout and X-Forward-For trusted hops) in the HTTP connection manager in a listener on the ingress gateway in istio-system namespace for the SNI host app.example.com:

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: hcm-tweaks
  namespace: istio-system
spec:
  workloadSelector:
    labels:
      istio: ingressgateway
  configPatches:
  - applyTo: NETWORK_FILTER # http connection manager is a filter in Envoy
    match:
      context: GATEWAY
      listener:
        filterChain:
          sni: app.example.com
          filter:
            name: "envoy.filters.network.http_connection_manager"
    patch:
      operation: MERGE
      value:
        common_http_protocol_options:
          idle_timeout: 30s
        xff_num_trusted_hops: 5

The following example inserts an attributegen filter that produces istio_operationId attribute which is consumed by the istio.stats fiter. filterClass: STATS encodes this dependency.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: reviews-request-operation
  namespace: myns
spec:
  workloadSelector:
    labels:
      app: reviews
  configPatches:
  - applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
    patch:
      operation: ADD
      filterClass: STATS # This filter will run *before* the Istio stats filter.
      value:
        name: istio.request_operation
        typed_config:
         "@type": type.googleapis.com/udpa.type.v1.TypedStruct
         type_url: type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
         value:
           config:
             configuration: |
               {
                 "attributes": [
                   {
                     "output_attribute": "istio_operationId",
                     "match": [
                       {
                         "value": "ListReviews",
                         "condition": "request.url_path == '/reviews' && request.method == 'GET'"
                       }]
                   }]
               }
             vm_config:
               runtime: envoy.wasm.runtime.null
               code:
                 local: { inline_string: "envoy.wasm.attributegen" }

The following example inserts an http ext_authz filter in the myns namespace.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: myns-ext-authz
  namespace: myns
spec:
  configPatches:
  - applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
    patch:
      operation: ADD
      filterClass: AUTHZ # This filter will run *after* the Istio authz filter.
      value:
        name: envoy.filters.http.ext_authz
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.http.ext_authz.v3.ExtAuthz
          grpc_service:
            envoy_grpc:
              cluster_name: acme-ext-authz
              initial_metadata:
              - key: foo
                value: myauth.acme # required by local ext auth server.

A workload in the myns namespace needs to access a different ext_auth server that does not accept initial metadata. Since proto merge cannot remove fields, the following configuration uses the REPLACE operation. If you do not need to inherit fields, REPLACE is preferred over MERGE.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: mysvc-ext-authz
  namespace: myns
spec:
  workloadSelector:
    labels:
      app: mysvc
  configPatches:
  - applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
    patch:
      operation: REPLACE
      value:
        name: envoy.filters.http.ext_authz
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.http.ext_authz.v3.ExtAuthz
          grpc_service:
            envoy_grpc:
              cluster_name: acme-ext-authz-alt

The following example deploys a Wasm extension for all inbound sidecar HTTP requests.

apiVersion: networking.istio.io/v1alpha3
kind: EnvoyFilter
metadata:
  name: wasm-example
  namespace: myns
spec:
  configPatches:
  # The first patch defines a named Wasm extension and provides a URL to fetch Wasm binary from,
  # and the binary configuration. It should come before the next patch that applies it.
  # This resource is visible to all proxies in the namespace "myns". It is possible to provide
  # multiple definitions for the same name "my-wasm-extension" in multiple namespaces. We recommend that:
  # - if overriding is desired, then the root level definition can be overriden per namespace with REPLACE.
  # - if overriding is not desired, then the name should be qualified with the namespace "myns/my-wasm-extension",
  #   to avoid accidental name collisions.
  - applyTo: EXTENSION_CONFIG
    patch:
      operation: ADD # REPLACE is also supported, and would override a cluster level resource with the same name.
      value:
        name: my-wasm-extension
        typed_config:
          "@type": type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm
          config:
            root_id: my-wasm-root-id
            vm_config:
              vm_id: my-wasm-vm-id
              runtime: envoy.wasm.runtime.v8
              code:
                remote:
                  http_uri:
                    uri: http://my-wasm-binary-uri
            configuration: |
              {}
  # The second patch instructs to apply the above Wasm filter to the listener/http connection manager.
  - applyTo: HTTP_FILTER
    match:
      context: SIDECAR_INBOUND
    patch:
      operation: ADD
      filterClass: AUTHZ # This filter will run *after* the Istio authz filter.
      value:
        name: my-wasm-extension # This must match the name above
        config_discovery:
          config_source:
            api_config_source:
              api_type: GRPC
              transport_api_version: V3
              grpc_services:
              - envoy_grpc:
                  cluster_name: xds-grpc
          type_urls: ["envoy.extensions.filters.http.wasm.v3.Wasm"]

EnvoyFilter

EnvoyFilter provides a mechanism to customize the Envoy configuration generated by Istio Pilot.

EnvoyFilter.ProxyMatch

One or more properties of the proxy to match on.

EnvoyFilter.ClusterMatch

Conditions specified in ClusterMatch must be met for the patch to be applied to a cluster.

EnvoyFilter.RouteConfigurationMatch

Conditions specified in RouteConfigurationMatch must be met for the patch to be applied to a route configuration object or a specific virtual host within the route configuration.

EnvoyFilter.ListenerMatch

Conditions specified in a listener match must be met for the patch to be applied to a specific listener across all filter chains, or a specific filter chain inside the listener.

EnvoyFilter.Patch

Patch specifies how the selected object should be modified.

EnvoyFilter.EnvoyConfigObjectMatch

One or more match conditions to be met before a patch is applied to the generated configuration for a given proxy.

EnvoyFilter.EnvoyConfigObjectPatch

Changes to be made to various envoy config objects.

EnvoyFilter.RouteConfigurationMatch.RouteMatch

Match a specific route inside a virtual host in a route configuration.

EnvoyFilter.RouteConfigurationMatch.VirtualHostMatch

Match a specific virtual host inside a route configuration.

EnvoyFilter.ListenerMatch.FilterChainMatch

For listeners with multiple filter chains (e.g., inbound listeners on sidecars with permissive mTLS, gateway listeners with multiple SNI matches), the filter chain match can be used to select a specific filter chain to patch.

EnvoyFilter.ListenerMatch.FilterMatch

Conditions to match a specific filter within a filter chain.

EnvoyFilter.ListenerMatch.SubFilterMatch

Conditions to match a specific filter within another filter. This field is typically useful to match a HTTP filter inside the envoy.filters.network.http_connection_manager network filter. This could also be applicable for thrift filters.

EnvoyFilter.RouteConfigurationMatch.RouteMatch.Action

Action refers to the route action taken by Envoy when a http route matches.

EnvoyFilter.Patch.Operation

Operation denotes how the patch should be applied to the selected configuration.

EnvoyFilter.Patch.FilterClass

FilterClass determines the filter insertion point in the filter chain relative to the filters implicitly inserted by the control plane. It is used in conjuction with the ADD operation. This is the preferred insertion mechanism for adding filters over the INSERT_* operations since those operations rely on potentially unstable filter names. Filter ordering is important if your filter depends on or affects the functioning of a another filter in the filter chain. Within a filter class, filters are inserted in the order of processing.

EnvoyFilter.ApplyTo

ApplyTo specifies where in the Envoy configuration, the given patch should be applied.

EnvoyFilter.PatchContext

PatchContext selects a class of configurations based on the traffic flow direction and workload type.