open-consul/website/source/docs/commands/connect/envoy.html.md.erb

---
layout: "docs"
page_title: "Commands: Connect Proxy"
sidebar_current: "docs-commands-connect-envoy"
description: >
  The connect proxy subcommand is used to run the built-in mTLS proxy for Connect.
---

# Consul Connect Envoy

Command: `consul connect envoy`

The connect Envoy command is used to generate a bootstrap configuration for
[Envoy proxy](https://envoyproxy.io) for use with [Consul
Connect](/docs/connect/).

The default behaviour is to generate the necessary bootstrap configuration for
Envoy based on the environment variables and options provided and by taking to
the local Consul agent. It `exec`s an external Envoy binary with that
configuration leaving the Envoy process running in the foreground. An error is
returned on operating systems other than linux or macOS since Envoy does not
build for other platforms currently.

If the `-bootstrap` option is specified, the bootstrap config is generated in
the same way and then printed to stdout. This allows it to be redirected to a
file and used with `envoy -c bootstrap.json`. This works on all operating
systems allowing configuration to be generated on a host that Envoy doesn't
build on but then used in a virtualized environment that can run Envoy.

## Usage

Usage: `consul connect envoy [options] [-- pass-through options]`

#### API Options

The standard API options are used to connect to the local agent to discover the
proxy configuration needed.

 - `-grpc-addr=<addr>` - Address of the Consul agent with `grpc` port. This can
   be an IP address or DNS address, but it must include the port. This can also
   be specified via the CONSUL_GRPC_ADDR environment variable. In Consul 1.3 and
   later, the default value is 127.0.0.1:8502, and https can optionally
   be used instead. The scheme can also be set to HTTPS by setting the
   environment variable CONSUL_HTTP_SSL=true. This may be a unix domain socket
   using `unix:///path/to/socket` if the [agent is configured to
   listen](/docs/agent/options.html#addresses) that way.

-> **Note:** gRPC uses the same TLS
   settings as the HTTPS API. If HTTPS is enabled then gRPC will require HTTPS
   as well.

   <%= partial "docs/commands/http_api_options_client" %>

#### Envoy Options

* `-sidecar-for` - The _ID_ (not name if they differ) of the service instance
  this proxy will represent. The target service doesn't need to exist on the
  local agent yet but a [sidecar proxy
  registration](/docs/connect/registration/service-registration.html) with
  `proxy.destination_service_id` equal to the passed value must be present. If
  multiple proxy registrations targeting the same local service instance are
  present the command will error and `-proxy-id` should be used instead.

* `-proxy-id` - The [proxy
  service](/docs/connect/registration/service-registration.html) ID on the
  local agent. This must already be present on the local agent.

-> **Note:** If ACLs are enabled, a token granting `service:write` for the
  _target_ service (configured in `proxy.destination_service_name`) must be
  passed using the `-token` option or `CONSUL_HTTP_TOKEN` environment variable.
  This token authorizes the proxy to obtain TLS certificates representing the
  target service.

 * `-envoy-binary` - The full path to a specific Envoy binary to exec. By
   default the current `$PATH` is searched for `envoy`.

 * `-admin-bind` - The `host:port` to bind Envoy's admin HTTP API. Default is
   `localhost:19000`. Envoy requires that this be enabled. The host part must be
   resolvable DNS name or IP address.

 * `-bootstrap` - If present, the command will simply output the generated
   bootstrap config to stdout in JSON protobuf form. This can be directed to a
   file and used to start Envoy with `envoy -c bootstrap.json`.

~> **Security Note:** If ACLs are enabled the bootstrap JSON will contain the
ACL token from `-token` or the environment and so should be handled as a secret.
This token grants the identity of any service it has `service:write` permission
for and so can be used to access any upstream service that that service is
allowed to access by [Connect intentions](/docs/connect/intentions.html).

 * `-- [pass-through options]` - Any options given after a double dash are passed
   directly through to the `envoy` invocation. See [Envoy's
   documentation](https://www.envoyproxy.io/docs) for more details. The command
   always specifies `--config-file` and `--v2-config-only` and by default passes
   `--disable-hot-restart` see [hot restart](#hot-restart).

## Examples

Assume a local service instance is registered on the local agent with a
sidecar proxy (using the [sidecar service
registration](/docs/connect/registration/service-registration.html) helper) as below.

```hcl
service {
  name = "web"
  port = 8080
  connect { sidecar_service {} }
}
```

The sidecar Envoy process can be started with.

```text
$ consul connect envoy -sidecar-for web
```

This example assumes that the correct [environment variables](#api-options) are
used to set the local agent connection information and ACL token, or that the
agent is using all-default configuration.

To pass additional arguments directly to Envoy, for example output logging
level, you can use:

```text
$ consul connect envoy -sidecar-for web -- -l debug
```

To run multiple different proxy instances on the same host, you will
need to use `-admin-bind` on all but one to ensure they don't attempt to bind to
the same port as in the following example.

```text
$ consul connect envoy -sidecar-for db -admin-bind localhost:19001
```

## Exec Security Details

The command needs to pass the bootstrap config through to Envoy. Envoy currently
only supports passing this as a file path or passing a whole string on the
command line with `--config-yaml`. Since the bootstrap needs to contain the ACL
token to authorize the proxy, this secret needs careful handling.

Passing a secret via command option is unacceptable as on many unix systems
these are readable to any user on the host for example via `/proc` or via a
setuid process like `ps`.

Creating a temporary file is more secure in that it can only be read by the
current user but risks leaving secret material on disk for an unbounded length
of time and in a location that is opaque to the operator.

To work around these issues, the command currently creates a temporary file and
immediately unlinks it so it can't be read by any other process that doesn't
already have the file descriptor. It then writes the bootstrap JSON, and unsets
the CLOEXEC bit on the file handle so that it remains available to the Envoy
process after exec. Finally it `exec`s Envoy with `--config-file /dev/fd/X`
where `X` is the the file descriptor number of the temp file.

This ensures that Envoy can read the file without any other normal user process
being able to (assuming they don't have privileged access to /proc). Once the
Envoy process stops, there is no longer any reference to the file to clean up.

## Envoy Hot Restart

Envoy supports hot restart which requires simple external coordination. By
default, this command will add `--disable-hot-restart` when it runs Envoy.

The reason for this default behavior is to make it easy to test and run local
demonstrations with multiple Envoy instances outside of cgroups or network
namespaces.

To use hot restart, Envoy needs to be started with either the `--restart-epoch`
option. If this command detects that option in the pass-through flags it will
_not_ add `--disable-hot-restart` allowing hot restart to work normally.

The only difference to note over running Envoy directly is that
`--restart-epoch` must be explicitly set to `0` for the initial launch of the
Envoy instance to avoid disabling hot restart entirely. The official
`hot-restarter.py` always sets this option so should work as recommended.