» 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 http/1.1, http2 or gRPC traffic at L7 or any other tcp-based protocol at L4. Prior to Consul 1.5.0 Envoy proxies could only proxy tcp at L4.

Currently configuration of additional L7 features is limited, however we have plans to support a wider range of features in the next major release cycle.

As an interim solution, you can add custom Envoy configuration in the proxy service definition allowing you to use the more powerful features of Envoy.

» Supported Versions

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

Consul Version Compatible Envoy Versions
1.5.x and higher 1.9.1, 1.8.0†
1.3.x, 1.4.x 1.9.1, 1.8.0†, 1.7.0†

» Getting Started

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

» Configuration

Envoy proxies require two types of configuration: an initial bootstrap configuration and 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 it's local Consul agent from which it discovers all of it's 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.
  • Service-discovery results for upstreams to enable each sidecar proxy to load-balance outgoing connections.
  • L7 configuration including timeouts and protocol-specific options.

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.

» 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 can generate it and then exec the Envoy binary as a convenience wrapper.

Because some Envoy configuration options like 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.

Users can 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.

    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. It is not currently possible to use environment variables as only part of the URL.

  • 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.

  • 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.

There are more possibilities available in the Advanced Configuration section 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.

Users can define a service's protocol in its 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.

» 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.
  • 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).

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

» Advanced Configuration

To support more flexibility when configuring Envoy, several "lower-level" options exist that exist that require knowledge of Envoy's configuration format. Many 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 it's protobuf JSON encoding. Advanced options are 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.

» 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.api.v2.Listener), or it may be the direct encoding with no @type field.

» 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.

» 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 it's security model.
  • envoy_public_listener_json - Specifies a complete 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.ext_authz filter prepended to the filters array to ensure that all inbound connections are authorized by Connect.
  • 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.

  • 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.