Envoy Integration

Consul Connect has first class support for using Envoy as a proxy. Consul configures Envoy by optionally exposing a gRPC service on the local agent that serves Envoy’s xDS configuration API.

Consul can configure Envoy sidecars to proxy traffic over the following protocols:

On Consul 1.5.0 and older, Envoy proxies can only proxy TCP traffic at L4.

Some L7 features can be configured using configuration entries. You can add custom Envoy configurations to the proxy service definition to use Envoy features that are not currently exposed through configuration entries. Adding custom Envoy configurations to the service definition is an interim solution that enables you to use the more powerful features of Envoy.

Note: When using Envoy with Consul and not using the consul connect envoy command Envoy must be run with the --max-obj-name-len option set to 256 or greater for Envoy versions prior to 1.11.0.

Supported Versions

Consul’s Envoy support was added in version 1.3.0. The following table shows compatible Envoy versions.

1. Use Consul 1.9.0+ with Envoy 1.15.0+ to ensure that intention enforcement is updated as quickly as possible after any changes. Additional information.
2. Envoy 1.10.0 requires setting -envoy-version in the consul connect envoy command. This was introduced in Consul 1.7.0.
3. Envoy 1.9.1 and older are vulnerable to CVE-2019-9900 and CVE-2019-9901. Both issues are related to parsing HTTP requests and only affect Consul Connect users if they have configured HTTP routing rules. We recommend that you use the most recent supported Envoy for your version of Consul when possible.

Getting Started

To get started with Envoy and see a working example you can follow the Using Envoy with Connect tutorial.

Configuration

Envoy proxies require two types of configuration: an initial bootstrap configuration and a dynamic configuration that is discovered from a “management server”, in this case Consul.

The bootstrap configuration at a minimum needs to configure the proxy with an identity (node id) and the location of its local Consul agent from which it discovers all of its dynamic configuration. See Bootstrap Configuration for more details.

The dynamic configuration Consul Connect provides to each Envoy instance includes:

• TLS certificates and keys to enable mutual authentication and keep certificates rotating.
• Intentions to enforce service-to-service authorization rules.
• Service-discovery results for upstreams to enable each sidecar proxy to load-balance outgoing connections.
• L7 configuration including timeouts and protocol-specific options.
• Configuration to expose specific HTTP paths.

For more information on the parts of the Envoy proxy runtime configuration that are currently controllable via Consul Connect see Dynamic Configuration.

We plan to enable more and more of Envoy’s features through Connect’s first-class configuration over time, however some advanced users will need additional control to configure Envoy in specific ways. To enable this, we provide several “escape hatch” options that allow users to provide low-level raw Envoy config syntax for some sub-components in each Envoy instance. This allows operators to have full control over and responsibility for correctly configuring Envoy and ensuring version support etc.

Intention Enforcement

Intentions are enforced using Envoy’s RBAC filters. Depending on the configured protocol of the proxied service, intentions are either enforced per-connection (L4) using a network filter, or per-request (L7) using an HTTP filter.

Note: Prior to Consul 1.9.0 intentions were exclusively enforced per-connection (L4) using an ext_authz network filter.

Fetching Certificates

Envoy will use the CONSUL_HTTP_TOKEN and CONSUL_HTTP_ADDR environment variables to contact Consul to fetch certificates if the following conditions are met:

• The CONSUL_HTTP_TOKEN environment variable contains a Consul ACL token.
• The Consul ACL token has the necessary permissions to read configuration for that service.

If TLS is enabled on Consul, you will also need to add the following environment variables prior to starting Envoy:

• CONSUL_CACERT
• CONSUL_CLIENT_CERT
• CONSUL_CLIENT_KEY
• CONSUL_HTTP_SSL

Bootstrap Configuration

Envoy requires an initial bootstrap configuration file. The easiest way to create this is using the consul connect envoy command. The command can either output the bootstrap configuration directly to stdout, or generate the configuration and issue an exec command to the Envoy binary as a convenience wrapper.

Because some Envoy configuration options, such as metrics and tracing sinks, can only be specified via the bootstrap configuration, Connect as of Consul 1.5.0 adds the ability to control some parts of the bootstrap config via proxy configuration options.

Add the following configuration items to the global proxy-defaults configuration entry or override them directly in the proxy.config field of a proxy service definition or sidecar_service block.

• envoy_statsd_url - A URL in the form udp://ip:port identifying a UDP StatsD listener that Envoy should deliver metrics to. For example, this may be udp://127.0.0.1:8125 if every host has a local StatsD listener. In this case users can configure this property once in the global proxy-defaults configuration entry for convenience. Currently, TCP is not supported.

  Note: currently the url must use an ip address not a dns name due to the way Envoy is setup for StatsD.

  Expansion of the environment variable HOST_IP is supported, e.g. udp://${HOST_IP}:8125.

  Users can also specify the whole parameter in the form $ENV_VAR_NAME, which will cause the consul connect envoy command to resolve the actual URL from the named environment variable when it runs. This, for example, allows each pod in a Kubernetes cluster to learn of a pod-specific IP address for StatsD when the Envoy instance is bootstrapped while still allowing global configuration of all proxies to use StatsD in the global proxy-defaults configuration entry. The env variable must contain a full valid URL value as specified above and nothing else.

• envoy_dogstatsd_url - The same as envoy_statsd_url with the following differences in behavior:

  • Envoy will use dogstatsd tags instead of statsd dot-separated metric names.
  • As well as udp://, a unix:// URL may be specified if your agent can listen on a unix socket (e.g. the dogstatsd agent).

• envoy_prometheus_bind_addr - Specifies that the proxy should expose a Prometheus metrics endpoint to the public network. It must be supplied in the form ip:port and port and the ip/port combination must be free within the network namespace the proxy runs. Typically the IP would be 0.0.0.0 to bind to all available interfaces or a pod IP address.

  Note: Envoy versions prior to 1.10 do not export timing histograms using the internal Prometheus endpoint.

• envoy_stats_bind_addr - Specifies that the proxy should expose the /stats prefix to the public network. It must be supplied in the form ip:port and the ip/port combination must be free within the network namespace the proxy runs. Typically the IP would be 0.0.0.0 to bind to all available interfaces or a pod IP address.

• envoy_stats_tags - Specifies one or more static tags that will be added to all metrics produced by the proxy.

• envoy_stats_flush_interval - Configures Envoy’s stats_flush_interval.

The Advanced Configuration section describes additional configurations that allow incremental or complete control over the bootstrap configuration generated.

Dynamic Configuration

Consul automatically generates Envoy’s dynamic configuration based on its knowledge of the cluster. Users may specify default configuration options for each service such as which protocol they speak. Consul will use this information to configure appropriate proxy settings for that service’s proxies and also for the upstream listeners of any downstream service.

One example is how users can define a service’s protocol in a service-defaults configuration entry. Agents with enable_central_service_config set to true will automatically discover the protocol when configuring a proxy for a service. The proxy will discover the main protocol of the service it represents and use this to configure its main public listener. It will also discover the protocols defined for any of its upstream services and automatically configure its upstream listeners appropriately too as below.

This automated discovery results in Consul auto-populating the proxy.config and proxy.upstreams[*].config fields of the proxy service definition that is actually registered.

To learn about other options that can be configured centrally see the Configuration Entries docs.

Proxy Config Options

These fields may also be overridden explicitly in the proxy service definition, or defined in the global proxy-defaults configuration entry to act as defaults that are inherited by all services.

• protocol - The protocol the service speaks. Connect’s Envoy integration currently supports the following protocol values:

  • tcp - Unless otherwise specified this is the default, which causes Envoy to proxy at L4. This provides all the security benefits of Connect’s mTLS and works for any TCP-based protocol. Load-balancing and metrics are available at the connection level.

  • http - This specifies that the service speaks HTTP/1.x. Envoy will setup an http_connection_manager and will be able to load-balance requests individually to available upstream services. Envoy will also emit L7 metrics such as request rates broken down by HTTP response code family (2xx, 4xx, 5xx, etc).

  • http2 - This specifies that the service speaks http2 (specifically h2c since Envoy will still only connect to the local service instance via plain TCP not TLS). This behaves much like http with L7 load-balancing and metrics but has additional settings that correctly enable end-to-end http2.

  • grpc - gRPC is a common RPC protocol based on http2. In addition to the http2 support above, Envoy listeners will be configured with a gRPC bridge filter that translates HTTP/1.1 calls into gRPC, and instruments metrics with gRPC-status trailer codes.

    Note: The protocol of a service should ideally be configured via the protocol field of a service-defaults config entry for the service. Configuring it in a proxy config will not fully enable some L7 features. It is supported here for backwards compatibility with Consul versions prior to 1.6.0.

• bind_address - Override the address Envoy’s public listener binds to. By default Envoy will bind to the service address or 0.0.0.0 if there is not explicit address on the service registration.

• bind_port - Override the port Envoy’s public listener binds to. By default Envoy will bind to the service port.

• local_connect_timeout_ms - The number of milliseconds allowed to make connections to the local application instance before timing out. Defaults to 5000 (5 seconds).

• local_request_timeout_ms - In milliseconds, the request timeout for HTTP requests to the local application instance. Applies to HTTP based protocols only. If not specified, inherits the Envoy default for route timeouts (15s). A value of 0 will disable request timeouts.

Proxy Upstream Config Options

The following configuration items may be overridden directly in the proxy.upstreams[].config field of a proxy service definition or sidecar_service block.

• protocol - Same as above in main config but affects the listener setup for the upstream.

  Note: The protocol of a service should ideally be configured via the protocol field of a service-defaults config entry for the upstream destination service. Configuring it in a proxy upstream config will not fully enable some L7 features. It is supported here for backwards compatibility with Consul versions prior to 1.6.0.

• connect_timeout_ms - The number of milliseconds to allow when making upstream connections before timing out. Defaults to 5000 (5 seconds).

  Note: The connection timeout for a service should ideally be configured via the connect_timeout field of a service-resolver config entry for the upstream destination service. Configuring it in a proxy upstream config will override any values defined in config entries. It is supported here for backwards compatibility with Consul versions prior to 1.6.0.

• limits - A set of limits to apply when connecting to the upstream service. These limits are applied on a per-service-instance basis. The following limits are respected:

  • max_connections - The maximum number of connections a service instance will be allowed to establish against the given upstream. Use this to limit HTTP/1.1 traffic, since HTTP/1.1 has a request per connection.
  • max_pending_requests - The maximum number of requests that will be queued while waiting for a connection to be established. For this configuration to be respected, a L7 protocol must be defined in the protocol field.
  • max_concurrent_requests - The maximum number of concurrent requests that will be allowed at a single point in time. Use this to limit HTTP/2 traffic, since HTTP/2 has many requests per connection. For this configuration to be respected, a L7 protocol must be defined in the protocol field.

• passive_health_check - Passive health checks are used to remove hosts from the upstream cluster which are unreachable or are returning errors.

  • interval - The time between checks. Each check will cause hosts which have exceeded max_failures to be removed from the load balancer, and any hosts which have passed their ejection time to be returned to the load balancer.
  • max_failures - The number of consecutive failures which cause a host to be removed from the load balancer.

Gateway Options

These fields may also be overridden explicitly in the proxy service definition, or defined in the global proxy-defaults configuration entry to act as defaults that are inherited by all services.

Prior to 1.8.0 these settings were specific to Mesh Gateways. The deprecated names such as envoy_mesh_gateway_bind_addresses and envoy_mesh_gateway_no_default_bind will continue to be supported.

• connect_timeout_ms - The number of milliseconds to allow when making upstream connections before timing out. Defaults to 5000 (5 seconds). If the upstream service has the configuration option connect_timeout_ms set for the service-resolver, that timeout value will take precedence over this gateway option.

• envoy_gateway_bind_tagged_addresses - Indicates that the gateway services tagged addresses should be bound to listeners in addition to the default listener address.

• envoy_gateway_bind_addresses - A map of additional addresses to be bound. This map’s keys are the name of the listeners to be created and the values are a map with two keys, address and port, that combined make the address to bind the listener to. These are bound in addition to the default address.

• envoy_gateway_no_default_bind - Prevents binding to the default address of the gateway service. This should be used with one of the other options to configure the gateway’s bind addresses.

• envoy_dns_discovery_type - Determines how Envoy will resolve hostnames. Defaults to LOGICAL_DNS. Must be one of STRICT_DNS or LOGICAL_DNS. Details for each type are available in the Envoy documentation. This option applies to terminating gateways that route to services addressed by a hostname, such as a managed database. It also applies to mesh gateways, such as when gateways in other Consul datacenters are behind a load balancer that is addressed by a hostname.

Advanced Configuration

To support more flexibility when configuring Envoy, several “lower-level” options exist that require knowledge of Envoy’s configuration format. Many options allow configuring a subsection of either the bootstrap or dynamic configuration using your own custom protobuf config.

We separate these into two sets, Advanced Bootstrap Options and Escape Hatch Overrides. Both require writing Envoy config in the protobuf JSON encoding. Advanced options cover smaller chunks that might commonly need to be set for tasks like configuring tracing. In contrast, escape hatches give almost complete control over the proxy setup, but require operators to manually code the entire configuration in protobuf JSON.

Advanced Topic! This section covers options that allow users to take almost complete control of Envoy’s configuration. We provide these options so users can experiment or take advantage of features not yet fully supported in Consul Connect. We plan to retain this ability in the future, but it should still be considered experimental because it requires in-depth knowledge of Envoy’s configuration format. Users should consider Envoy version compatibility when using these features because they can configure Envoy in ways that are outside of Consul’s control. Incorrect configuration could prevent all proxies in your mesh from functioning correctly, or bypass the security guarantees Connect is designed to enforce.

Configuration Formatting

All configurations are specified as strings containing the serialized proto3 JSON encoding of the specified Envoy configuration type. They are full JSON types except where noted.

The JSON supplied may describe a protobuf types.Any message with an @type field set to the appropriate type (for example type.googleapis.com/envoy.config.listener.v3.Listener).

For example, given a tracing config:

{
  "http": {
    "name": "envoy.tracers.zipkin",
    "typedConfig": {
      "@type": "type.googleapis.com/envoy.config.trace.v3.ZipkinConfig",
      "collector_cluster": "zipkin",
      "collector_endpoint_version": "HTTP_JSON",
      "collector_endpoint": "/api/v1/spans",
      "shared_span_context": false
    }
  }
}

JSON escape the value of tracing into a string, for example using https://codebeautify.org/json-escape-unescape, or using jq.

$ cat <<EOF | jq '. | @json'
{
  "http": {
    "name": "envoy.tracers.zipkin",
    "typedConfig": {
      "@type": "type.googleapis.com/envoy.config.trace.v3.ZipkinConfig",
      "collector_cluster": "zipkin",
      "collector_endpoint_version": "HTTP_JSON",
      "collector_endpoint": "/api/v1/spans",
      "shared_span_context": false
    }
  }
}
EOF
"{\"http\":{\"name\":\"envoy.tracers.zipkin\",\"typedConfig\":{\"@type\":\"type.googleapis.com/envoy.config.trace.v3.ZipkinConfig\",\"collector_cluster\":\"zipkin\",\"collector_endpoint_version\":\"HTTP_JSON\",\"collector_endpoint\":\"/api/v1/spans\",\"shared_span_context\":false}}}"

Then use that as the value for envoy_tracing_json:

{
  "kind": "proxy-defaults",
  "name": "global",
  "config": {
    "envoy_tracing_json": "{\"http\":{\"name\":\"envoy.tracers.zipkin\",\"typedConfig\":{\"@type\":\"type.googleapis.com/envoy.config.trace.v3.ZipkinConfig\",\"collector_cluster\":\"zipkin\",\"collector_endpoint_version\":\"HTTP_JSON\",\"collector_endpoint\":\"/api/v1/spans\",\"shared_span_context\":false}}}\n"
  }
}

If using HCL, this escaping is done automatically:

Kind = "proxy-defaults"
Name = "global"
Config {
  envoy_tracing_json = <<EOF
{
  "http": {
    "name": "envoy.tracers.zipkin",
    "typedConfig": {
      "@type": "type.googleapis.com/envoy.config.trace.v3.ZipkinConfig",
      "collector_cluster": "zipkin",
      "collector_endpoint_version": "HTTP_JSON",
      "collector_endpoint": "/api/v1/spans",
      "shared_span_context": false
    }
  }
}
EOF
}

Advanced Bootstrap Options

Users may add the following configuration items to the global proxy-defaults configuration entry or override them directly in the proxy.config field of a proxy service definition or sidecar_service block.

• envoy_extra_static_clusters_json - Specifies one or more Envoy clusters that will be appended to the array of static clusters in the bootstrap config. This allows adding custom clusters for tracing sinks for example. For a single cluster just encode a single object, for multiple, they should be comma separated with no trailing comma suitable for interpolating directly into a JSON array inside the braces.

• envoy_extra_static_listeners_json - Similar to envoy_extra_static_clusters_json but appends one or more Envoy listeners to the array of static listener definitions. Can be used to setup limited access that bypasses Connect mTLS or authorization for health checks or metrics.

• envoy_extra_stats_sinks_json - Similar to envoy_extra_static_clusters_json but for stats sinks. These are appended to any sinks defined by use of the higher-level envoy_statsd_url or envoy_dogstatsd_url config options.

• envoy_stats_config_json - The entire stats config. If provided this will override the higher-level envoy_stats_tags. It allows full control over dynamic tag replacements etc.

• envoy_tracing_json - The entire tracing config. Most tracing providers will also require adding static clusters to define the endpoints to send tracing data to.

Escape-Hatch Overrides

Users may add the following configuration items to the global proxy-defaults configuration entry or override them directly in the proxy.config field of a proxy service definition or sidecar_service block.

• envoy_bootstrap_json_tpl - Specifies a template in Go template syntax that is used in place of the default template when generating bootstrap via consul connect envoy command. The variables that are available to be interpolated are documented here. This offers complete control of the proxy’s bootstrap although major deviations from the default template may break Consul’s ability to correctly manage the proxy or enforce its security model.

• envoy_public_listener_json - Specifies a complete Envoy listener to be delivered in place of the main public listener that the proxy used to accept inbound connections. This will be used verbatim with the following exceptions:

  • Every FilterChain added to the listener will have its TlsContext overridden by the Connect TLS certificates and validation context. This means there is no way to override Connect’s mutual TLS for the public listener.
  • Every FilterChain will have the envoy.filters.{network|http}.rbac filter prepended to the filters array to ensure that all inbound connections are authorized by Connect. Before Consul 1.9.0 envoy.ext_authz was inserted instead.
• envoy_local_cluster_json - Specifies a complete Envoy cluster to be delivered in place of the local application cluster. This allows customization of timeouts, rate limits, load balancing strategy etc.

The following configuration items may be overridden directly in the proxy.upstreams[].config field of a proxy service definition or sidecar_service block.

Note: - When a service-router, service-splitter, or service-resolver config entry exists for a service the below escape hatches are ignored and will log a warning.

• envoy_listener_json - Specifies a complete Listener to be delivered in place of the upstream listener that the proxy exposes to the application for outbound connections. This will be used verbatim with the following exceptions:

  • Every FilterChain added to the listener will have its TlsContext overridden by the Connect TLS certificates and validation context. This means there is no way to override Connect’s mutual TLS for the public listener.
• envoy_cluster_json - Specifies a complete Envoy cluster to be delivered in place of the discovered upstream cluster. This allows customization of timeouts, circuit breaking, rate limits, load balancing strategy etc.