--- title: Envoy Filter description: Customizing Envoy configuration generated by Istio. location: https://istio.io/docs/reference/config/networking/envoy-filter.html layout: protoc-gen-docs generator: protoc-gen-docs schema: istio.networking.v1alpha3.EnvoyFilter aliases: [/docs/reference/config/networking/v1alpha3/envoy-filter] number_of_entries: 18 ---

`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 are 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 typed_config section.
            name: "envoy.extensions.filters.network.mongo_proxy"
            typed_config:
              "@type": "type.googleapis.com/envoy.extensions.filters.network.mongo_proxy.v3.MongoProxy"
              ...
      - 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
            filterChain:
              filter:
                name: "envoy.filters.network.http_connection_manager"
                subFilter:
                  name: "envoy.filters.http.router"
        patch:
          operation: INSERT_BEFORE
          value: # lua filter specification
           name: envoy.filters.http.lua
           typed_config:
              "@type": "type.googleapis.com/envoy.extensions.filters.http.lua.v3.Lua"
              defaultSourceCode:
                inlineString: |
                  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
            load_assignment:
              cluster_name: lua_cluster
              endpoints:
              - lb_endpoints:
                - endpoint:
                    address:
                      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:
            typed_config:
              "@type": "type.googleapis.com/envoy.extensions.filters.network.http_connection_manager.v3.HttpConnectionManager"
              xff_num_trusted_hops: 5
              common_http_protocol_options:
                idle_timeout: 30s

The following example inserts an attributegen filter that produces `istio_operationId` attribute which is consumed by the istio.stats filter. `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 overridden 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
          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:
                  "@type": "type.googleapis.com/google.protobuf.StringValue"
                  value: |
                    {}
      # The second patch instructs to apply the above Wasm filter to the listener/http connection manager.
      - applyTo: HTTP_FILTER
        match:
          listener:
            filterChain:
              filter:
                name: envoy.filters.network.http_connection_manager
                subFilter:
                  name: envoy.filters.http.router
        patch:
          operation: INSERT_BEFORE
          value:
            name: my-wasm-extension # This must match the name above
            config_discovery:
              config_source:
                ads: {}
              type_urls: ["type.googleapis.com/envoy.extensions.filters.http.wasm.v3.Wasm"]

The following example inserts an `envoy.filters.listener.proxy_protocol` listener filter before the `envoy.filters.listener.tls_inspector`.

    apiVersion: networking.istio.io/v1alpha3
    kind: EnvoyFilter
    metadata:
      name: listener-filter-example
      namespace: myns
    spec:
      configPatches:
      - applyTo: LISTENER_FILTER
        match:
          context: SIDECAR_INBOUND # will match inbound listeners in all sidecars
          listener:
            portNumber: 15006
            listenerFilter: "envoy.filters.listener.tls_inspector"
        patch:
          operation: INSERT_BEFORE
          value:
            # This is the full filter config including the name and typed_config section.
            name: "envoy.filters.listener.proxy_protocol"
            typed_config:
              "@type": "type.googleapis.com/envoy.extensions.filters.listener.proxy_protocol.v3.ProxyProtocol"

## EnvoyFilter

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

Field | Type | Description | Required
--- | --- | --- | ---
`workloadSelector` | `WorkloadSelector` | Criteria used to select the specific set of pods/VMs on which this patch configuration should be applied. If omitted, the set of patches in this configuration will be applied to all workload instances in the same namespace. If the `EnvoyFilter` is present in the config root namespace, it will be applied to all applicable workloads in any namespace. | No
`targetRefs` | `PolicyTargetReference[]` | Optional. The targetRefs specifies a list of resources the policy should be applied to. The targeted resources specified will determine which workloads the policy applies to. Currently, the following resource attachment types are supported: `kind: Gateway` with `group: gateway.networking.k8s.io` in the same namespace. `kind: Service` with `""` in the same namespace. This type is only supported for waypoints. If not set, the policy is applied as defined by the selector. At most one of the selector and targetRefs can be set. NOTE: If you are using the `targetRefs` field in a multi-revision environment with Istio versions prior to 1.22, it is highly recommended that you pin the policy to a revision running 1.22+ via the `istio.io/rev` label. This is to prevent proxies connected to older control planes (that don’t know about the `targetRefs` field) from misinterpreting the policy as namespace-wide during the upgrade process. NOTE: Waypoint proxies are required to use this field for policies to apply; `selector` policies will be ignored. | No
`configPatches` | `EnvoyConfigObjectPatch[]` | One or more patches with match conditions. | No
`priority` | `int32` | Priority defines the order in which patch sets are applied within a context. When one patch depends on another patch, the order of patch application is significant. The API provides two primary ways to order patches. Patch sets in the root namespace are applied before the patch sets in the workload namespace. Patches within a patch set are processed in the order that they appear in the `configPatches` list. The default value for priority is 0 and the range is [ min-int32, max-int32 ]. A patch set with a negative priority is processed before the default. A patch set with a positive priority is processed after the default. It is recommended to start with priority values that are multiples of 10 to leave room for further insertion. Patch sets are sorted in the following ascending key order: priority, creation time, fully qualified resource name. | No

## EnvoyFilter.ProxyMatch

One or more properties of the proxy to match on.

Field | Type | Description | Required
--- | --- | --- | ---
`proxyVersion` | `string` | A regular expression in golang regex format (RE2) that can be used to select proxies using a specific version of istio proxy. The Istio version for a given proxy is obtained from the node metadata field `ISTIO_VERSION` supplied by the proxy when connecting to Pilot. This value is embedded as an environment variable (`ISTIO_META_ISTIO_VERSION`) in the Istio proxy docker image. Custom proxy implementations should provide this metadata variable to take advantage of the Istio version check option. | No
`metadata` | `map<string, string>` | Match on the node metadata supplied by a proxy when connecting to Istio Pilot. Note that while Envoy’s node metadata is of type Struct, only string key-value pairs are processed by Pilot. All keys specified in the metadata must match with exact values. The match will fail if any of the specified keys are absent or the values fail to match. | No

## EnvoyFilter.ClusterMatch

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

Field | Type | Description | Required
--- | --- | --- | ---
`portNumber` | `uint32` | The service port for which this cluster was generated. If omitted, applies to clusters for any port. Note: for inbound cluster, it is the service target port. | No
`service` | `string` | The fully qualified service name for this cluster. If omitted, applies to clusters for any service. For services defined through service entries, the service name is same as the hosts defined in the service entry. Note: for inbound cluster, this is ignored. | No
`subset` | `string` | The subset associated with the service. If omitted, applies to clusters for any subset of a service. | No
`name` | `string` | The exact name of the cluster to match. To match a specific cluster by name, such as the internally generated `Passthrough` cluster, leave all fields in clusterMatch empty, except the name. | No

## 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.

Field | Type | Description | Required
--- | --- | --- | ---
`portNumber` | `uint32` | The service port number or gateway server port number for which this route configuration was generated. If omitted, applies to route configurations for all ports. | No
`portName` | `string` | Applicable only for GATEWAY context. The gateway server port name for which this route configuration was generated. | No
`gateway` | `string` | The Istio gateway config’s namespace/name for which this route configuration was generated. Applies only if the context is GATEWAY. Should be in the namespace/name format. Use this field in conjunction with the `portNumber` and `portName` to accurately select the Envoy route configuration for a specific HTTPS server within a gateway config object. | No
`vhost` | `VirtualHostMatch` | Match a specific virtual host in a route configuration and apply the patch to the virtual host. | No
`name` | `string` | Route configuration name to match on. Can be used to match a specific route configuration by name, such as the internally generated `http_proxy` route configuration for all sidecars. | No

## 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.

Field | Type | Description | Required
--- | --- | --- | ---
`portNumber` | `uint32` | The service port/gateway port to which traffic is being sent/received. If not specified, matches all listeners. Even though inbound listeners are generated for the instance/pod ports, only service ports should be used to match listeners. | No
`filterChain` | `FilterChainMatch` | Match a specific filter chain in a listener. If specified, the patch will be applied to the filter chain (and a specific filter if specified) and not to other filter chains in the listener. | No
`listenerFilter` | `string` | Match a specific listener filter. If specified, the patch will be applied to the listener filter. | No
`name` | `string` | Match a specific listener by its name. The listeners generated by Pilot are typically named as IP:Port. | No

## EnvoyFilter.Patch

Patch specifies how the selected object should be modified.

Field | Type | Description | Required
--- | --- | --- | ---
`operation` | `Operation` | Determines how the patch should be applied. | No
`value` | `Struct` | The JSON config of the object being patched. This will be merged using proto merge semantics with the existing proto in the path. | No
`filterClass` | `FilterClass` | Determines the filter insertion order. | No

## EnvoyFilter.EnvoyConfigObjectMatch

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

Field | Type | Description | Required
--- | --- | --- | ---
`context` | `PatchContext` | The specific config generation context to match on. Istio Pilot generates envoy configuration in the context of a gateway, inbound traffic to sidecar and outbound traffic from sidecar. | No
`proxy` | `ProxyMatch` | Match on properties associated with a proxy. | No
`listener` | `ListenerMatch (oneof)` | Match on envoy listener attributes. | No
`routeConfiguration` | `RouteConfigurationMatch (oneof)` | Match on envoy HTTP route configuration attributes. | No
`cluster` | `ClusterMatch (oneof)` | Match on envoy cluster attributes. | No

## EnvoyFilter.EnvoyConfigObjectPatch

Changes to be made to various envoy config objects.

Field | Type | Description | Required
--- | --- | --- | ---
`applyTo` | `ApplyTo` | Specifies where in the Envoy configuration, the patch should be applied. The match is expected to select the appropriate object based on applyTo. For example, an applyTo with `HTTP_FILTER` is expected to have a match condition on the listeners, with a network filter selection on `envoy.filters.network.http_connection_manager` and a sub filter selection on the HTTP filter relative to which the insertion should be performed. Similarly, an applyTo on `CLUSTER` should have a match (if provided) on the cluster and not on a listener. | No
`match` | `EnvoyConfigObjectMatch` | Match on listener/route configuration/cluster. | No
`patch` | `Patch` | The patch to apply along with the operation. | No

## EnvoyFilter.RouteConfigurationMatch.RouteMatch

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

Field | Type | Description | Required
--- | --- | --- | ---
`name` | `string` | The Route objects generated by default are named as default. Route objects generated using a virtual service will carry the name used in the virtual service’s HTTP routes. | No
`action` | `Action` | Match a route with specific action type. | No

## EnvoyFilter.RouteConfigurationMatch.VirtualHostMatch

Match a specific virtual host inside a route configuration.

Field | Type | Description | Required
--- | --- | --- | ---
`name` | `string` | The VirtualHosts objects generated by Istio are named as host:port, where the host typically corresponds to the VirtualService’s host field or the hostname of a service in the registry. | No
`route` | `RouteMatch` | Match a specific route within the virtual host. | No

## 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.

Field | Type | Description | Required
--- | --- | --- | ---
`name` | `string` | The name assigned to the filter chain. | No
`sni` | `string` | The SNI value used by a filter chain’s match condition. This condition will evaluate to false if the filter chain has no sni match. | No
`transportProtocol` | `string` | Applies only to `SIDECAR_INBOUND` context. If non-empty, a transport protocol to consider when determining a filter chain match. This value will be compared against the transport protocol of a new connection, when it’s detected by the `tls_inspector` listener filter. Accepted values include: `raw_buffer` - default, used when no transport protocol is detected. `tls` - set when TLS protocol is detected by the TLS inspector. | No
`applicationProtocols` | `string` | Applies only to sidecars. If non-empty, a comma separated set of application protocols to consider when determining a filter chain match. This value will be compared against the application protocols of a new connection, when it’s detected by one of the listener filters such as the `http_inspector`. Accepted values include: h2, http/1.1, http/1.0 | No
`filter` | `FilterMatch` | The name of a specific filter to apply the patch to. Set this to `envoy.filters.network.http_connection_manager` to add a filter or apply a patch to the HTTP connection manager. | No
`destinationPort` | `uint32` | The destination_port value used by a filter chain’s match condition. This condition will evaluate to false if the filter chain has no destination_port match. | No

## EnvoyFilter.ListenerMatch.FilterMatch

Conditions to match a specific filter within a filter chain.

Field | Type | Description | Required
--- | --- | --- | ---
`name` | `string` | The filter name to match on. For standard Envoy filters, canonical filter names should be used. | No
`subFilter` | `SubFilterMatch` | The next level filter within this filter to match upon. Typically used for HTTP Connection Manager filters and Thrift filters. | No

## 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.

Field | Type | Description | Required
--- | --- | --- | ---
`name` | `string` | The filter name to match on. | No

## EnvoyFilter.RouteConfigurationMatch.RouteMatch.Action

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

Name | Description
--- | ---
`ANY` | All three route actions
`ROUTE` | Route traffic to a cluster / weighted clusters.
`REDIRECT` | Redirect request.
`DIRECT_RESPONSE` | directly respond to a request with specific payload.

## EnvoyFilter.Patch.Operation

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

Name | Description
--- | ---
`INVALID` |
`MERGE` | Merge the provided config with the generated config using proto merge semantics. If you are specifying config in its entirety, use `REPLACE` instead.
`ADD` | Add the provided config to an existing list (of listeners, clusters, virtual hosts, network filters, or http filters). This operation will be ignored when `applyTo` is set to `ROUTE_CONFIGURATION`, or `HTTP_ROUTE`.
`REMOVE` | Remove the selected object from the list (of listeners, clusters, virtual hosts, network filters, routes, or http filters). Does not require a value to be specified. This operation will be ignored when `applyTo` is set to `ROUTE_CONFIGURATION`, or `HTTP_ROUTE`.
`INSERT_BEFORE` | Insert operation on an array of named objects. This operation is typically useful only in the context of filters or routes, where the order of elements matter. Routes should be ordered based on most to least specific matching criteria since the first matching element is selected. For clusters and virtual hosts, order of the element in the array does not matter. Insert before the selected filter or sub filter. If no filter is selected, the specified filter will be inserted at the front of the list.
`INSERT_AFTER` | Insert operation on an array of named objects. This operation is typically useful only in the context of filters or routes, where the order of elements matter. Routes should be ordered based on most to least specific matching criteria since the first matching element is selected. For clusters and virtual hosts, order of the element in the array does not matter. Insert after the selected filter or sub filter. If no filter is selected, the specified filter will be inserted at the end of the list.
`INSERT_FIRST` | Insert operation on an array of named objects. This operation is typically useful only in the context of filters or routes, where the order of elements matter. Routes should be ordered based on most to least specific matching criteria since the first matching element is selected. For clusters and virtual hosts, order of the element in the array does not matter. Insert first in the list based on the presence of selected filter or not. This is specifically useful when you want your filter first in the list based on a match condition specified in Match clause.
`REPLACE` | Replace contents of a named filter with new contents. `REPLACE` operation is only valid for `HTTP_FILTER` and `NETWORK_FILTER`. If the named filter is not found, this operation has no effect.

## 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 conjunction 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.

Name | Description
--- | ---
`UNSPECIFIED` | Control plane decides where to insert the filter. Do not specify `FilterClass` if the filter is independent of others.
`AUTHN` | Insert filter after Istio authentication filters.
`AUTHZ` | Insert filter after Istio authorization filters.
`STATS` | Insert filter before Istio stats filters.

## EnvoyFilter.ApplyTo

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

Name | Description
--- | ---
`INVALID` |
`LISTENER` | Applies the patch to the listener.
`FILTER_CHAIN` | Applies the patch to the filter chain.
`NETWORK_FILTER` | Applies the patch to the network filter chain, to modify an existing filter or add a new filter.
`HTTP_FILTER` | Applies the patch to the HTTP filter chain in the http connection manager, to modify an existing filter or add a new filter.
`ROUTE_CONFIGURATION` | Applies the patch to the Route configuration (rds output) inside a HTTP connection manager. This does not apply to the virtual host. Currently, only `MERGE` operation is allowed on the route configuration objects.
`VIRTUAL_HOST` | Applies the patch to a virtual host inside a route configuration.
`HTTP_ROUTE` | Applies the patch to a route object inside the matched virtual host in a route configuration.
`CLUSTER` | Applies the patch to a cluster in a CDS output. Also used to add new clusters.
`EXTENSION_CONFIG` | Applies the patch to or adds an extension config in ECDS output. Note that ECDS is only supported by HTTP filters.
`BOOTSTRAP` | DEPRECATED. Applies the patch to bootstrap configuration.
`LISTENER_FILTER` | Applies the patch to the listener filter.

## EnvoyFilter.PatchContext

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

Name | Description
--- | ---
`ANY` | All listeners/routes/clusters in both sidecars and gateways.
`SIDECAR_INBOUND` | Inbound listener/route/cluster in sidecar.
`SIDECAR_OUTBOUND` | Outbound listener/route/cluster in sidecar.
`GATEWAY` | Gateway listener/route/cluster.