Envoy Filter

13 minute read

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 gateays 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.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.http_connection_manager"
    patch:
      operation: MERGE
      value:
        name: "envoy.http_connection_manager"
        typed_config:
          "@type": "type.googleapis.com/envoy.config.filter.network.http_connection_manager.v2.HttpConnectionManager"
          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.http_connection_manager"
            subFilter:
              name: "envoy.router"
    patch:
      operation: INSERT_BEFORE
      value: # lua filter specification
       name: envoy.lua
       typed_config:
          "@type": "type.googleapis.com/envoy.config.filter.http.lua.v2.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: ingress-gateway
  configPatches:
  - applyTo: NETWORK_FILTER # http connection manager is a filter in Envoy
    match:
      context: GATEWAY
      listener:
        filterChain:
          sni: app.example.com
          filter:
            name: "envoy.http_connection_manager"
    patch:
      operation: MERGE
      value:
        idle_timeout: 30s
        xff_num_trusted_hops: 5

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 omitted, the EnvoyFilter patches will be applied to all workloads 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
`configPatches`	`EnvoyConfigObjectPatch[]`	One or more patches with match conditions.	Yes

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. Currently, only MERGE operation is allowed on the route objects.
`CLUSTER`	Applies the patch to a cluster in a CDS output. Also used to add new clusters.

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.	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.	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.DeprecatedListenerMatch.ListenerProtocol

Name	Description
`ALL`	All protocols
`HTTP`	HTTP or HTTPS (with termination) / HTTP2/gRPC
`TCP`	Any non-HTTP listener

EnvoyFilter.DeprecatedListenerMatch.ListenerType

Name	Description
`ANY`	All listeners
`SIDECAR_INBOUND`	Inbound listener in sidecar
`SIDECAR_OUTBOUND`	Outbound listener in sidecar
`GATEWAY`	Gateway listener

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.	Yes
`routeConfiguration`	`RouteConfigurationMatch (oneof)`	Match on envoy HTTP route configuration attributes.	Yes
`cluster`	`ClusterMatch (oneof)`	Match on envoy cluster attributes.	Yes

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 HTTPFILTER is expected to have a match condition on the listeners, with a network filter selection on envoy.httpconnection_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.Filter.FilterType

Name	Description
`INVALID`	placeholder
`HTTP`	Http filter
`NETWORK`	Network filter

EnvoyFilter.InsertPosition.Index

Index/position in the filter chain.

Name	Description
`FIRST`	Insert first
`LAST`	Insert last
`BEFORE`	Insert before the named filter.
`AFTER`	Insert after the named filter.

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
`name`	`string`	Match a specific listener by its name. The listeners generated by Pilot are typically named as IP:Port.	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 SIDECARINBOUND 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 tlsinspector 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.httpconnectionmanager to add a filter or apply a patch to the HTTP connection manager.	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.	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.httpconnectionmanager network filter. This could also be applicable for thrift filters.

Field	Type	Description	Required
`name`	`string`	The filter name to match on.	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 json merge semantics with the existing proto in the path.	No

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 json merge semantics.
`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 ROUTECONFIGURATION, or HTTPROUTE.
`REMOVE`	Remove the selected object from the list (of listeners, clusters, virtual hosts, network filters, or http filters). Does not require a value to be specified. This operation will be ignored when applyTo is set to ROUTECONFIGURATION, or HTTPROUTE.
`INSERT_BEFORE`	Insert operation on an array of named objects. This operation is typically useful only in the context of filters, where the order of filters matter. 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, where the order of filters matter. 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, where the order of filters matter. 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.

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.

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 ISTIOVERSION supplied by the proxy when connecting to Pilot. This value is embedded as an environment variable (ISTIOMETAISTIOVERSION) 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.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.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.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.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

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