---
name: Secure Service-to-Service Communication
content_length: 12
id: connect-services
products_used:
  - Consul
description: This guide demonstrates Consul Connect using internal proxies as sidecars.
level: Implementation
---

Consul Connect secures service-to-service communication with authorization and
encryption. Applications can use sidecar proxies in a service mesh
configuration to automatically establish TLS connections for inbound and
outbound connections without being aware of Connect at all. In addition to
securing your services, Connect can also intercept [data about service-to-service
communications][consul-l7] and surface it to monitoring tools.

In this guide, you will register two services and their [sidecar] proxies in
the Consul catalog. You will then start the services and sidecar proxies.
Finally, you will demonstrate that the service-to-service communication is going
through the proxies by stopping traffic with an "[intention]".

[![Flow diagram showing end user traffic being sent to the Dashboard Service at
port 9002. The dashboard service makes requests for the counting service to the
local Connect Proxy at port 5000. This traffic then traverses the Connect mesh
over dynamic ports. The traffic exits the Connect mesh from the counting service's
local proxy. The proxy sends this traffic to the counting service itself at port
9003.][img-flow]][img-flow]

While this guide uses elements that are not suitable for production
environments—Consul dev agents, internal proxies, and mock services—it will
teach you the common process for deploying your own services using Consul
Connect. At the end of this guide, we also present additional information
about adapting this process to more production-like environments.

## Prerequisites

To complete this guide, you will need a local [dev agent], which enables
Connect by default.

This guide uses the following example service applications. Download and unzip
the executables to follow along.

- [Counting Service]
- [Dashboard Service]

### Verify your Consul agent health

To ensure that Consul is running and accessible from the command line, use the
`consul members` command to verify your agent status.

```shell-session
$ consul members
Node            Address         Status  Type    Build  Protocol  DC   Segment
hostname.local  127.0.0.1:8301  alive   server  1.6.1  2         dc1  <all>
```

If you receive an error message, verify that you have a local Consul dev agent
running and try again.

## Register the services and sidecar proxies

Services have to be registered with Consul. Consul shares this information
around the cluster so that operators or other services can determine the
location of a service. Connect also uses service registrations to determine
where to send proxied traffic to.

There are several ways to register services in Consul:

- directly from a Consul-aware application

- from an orchestrator, like [Nomad][services-nomad] or [Kubernetes][services-k8s]

- [using configuration files][services-config] that are loaded at node startup

- [using the API][services-api] to register them with a JSON or HCL
  specification

- [using the CLI][services-cli] to simplify this submission process

For this guide, we will use the [`consul service register`][services-cli] CLI
command to load them into the catalog.

### Create the counting service definition

First, define the Counting service and its sidecar proxy in a file named
`counting.hcl`. The definition should include the name of the service, the port
the service listens on, and a [connect] block with the [sidecar_service] block.
This block is empty so Consul will use default parameters. The definition also
includes an optional service health check.

```hcl
service {
  name = "counting"
  id = "counting-1"
  port = 9003

  connect {
    sidecar_service {}
  }

  check {
    id       = "counting-check"
    http     = "http://localhost:9003/health"
    method   = "GET"
    interval = "1s"
    timeout  = "1s"
  }
}
```

Services and sidecar proxies can be defined in either HCL or JSON. There is a
[JSON version][counting-1.json] version of the service definition in the
[demo-consul-101 project].

### Create the dashboard service definition

Create the Dashboard service and proxy definition in the same way. First,
create a file named `dashboard.hcl`.

```hcl
service {
  name = "dashboard"
  port = 9002

  connect {
    sidecar_service {
      proxy {
        upstreams = [
          {
            destination_name = "counting"
            local_bind_port  = 5000
          }
        ]
      }
    }
  }

  check {
    id       = "dashboard-check"
    http     = "http://localhost:9002/health"
    method   = "GET"
    interval = "1s"
    timeout  = "1s"
  }
}
```

There is a [JSON version][dashboard.json] of the service definition in the
[demo-consul-101 project].

Notice that the dashboard definition also includes an upstream block. Upstreams
are ports on the local host that will be proxied to the destination service.
The upstream block's local_bind_port value is the port your service will
communicate with to reach the service you depend on. The destination name is
the Consul service name that the local_bind_port will proxy to.

In our scenario, the dashboard service depends on the counting service. With
this configuration, when dashboard service connects to localhost:5000 it is
proxied across the service mesh to the counting service.

### Register the services and proxies

Finally, you can submit the service definitions to your Consul agent. If you
are using the JSON definitions, ensure that the filenames end in ".json"
instead of ".hcl".

```shell-session
$ consul services register counting.hcl
Registered service: counting
```

```shell-session
$ consul services register dashboard.hcl
Registered service: dashboard
```

-> **Challenge:** After completing the guide, try doing it again using one of
the other service registration mechanisms mentioned earlier in the guide to
register the services.

### Verify the services are registered

Now that you have registered your services and sidecar proxies, run `consul catalog services` to verify that they are present.

```shell-session
$ consul catalog services
consul
counting
counting-sidecar-proxy
dashboard
dashboard-sidecar-proxy
```

### Create a Connect intention

Intentions define access control for services via Connect and are used to
control which services may establish connections. The default intention
behavior is defined by the [default ACL policy].

In this guide, this step is not necessary since the default ACL policy of the
dev agent is "allow all", so Connect connections are automatically allowed as
well. However, we will create explicit intentions as a part of deploying
Connect-enabled services.

-> **Best Practice:** Creating an explicit intention helps protect your
service against changes to the implied permissions. For example, a change in
`default_policy` or the introduction of a global deny-all intention would
impact services without explicit intentions defined.

```shell-session
$ consul intention create dashboard counting
Created: dashboard => counting (allow)
```

## Start the services and sidecar proxies

Now that you have created all the necessary configuration to describe your
service's connections, it's time to start your services and their sidecar
proxies. We are using the `&` operator to run the services as background tasks.
However, because they write to the console, it's best to run them in their own
shell session.

Run these commands to start the applications:

```shell-session
$ PORT=9002 COUNTING_SERVICE_URL="http://localhost:5000" ./dashboard-service &
$ PORT=9003 ./counting-service &
```

Next, start the sidecar proxies that will run as [sidecar] processes along with
the service applications.

We are using the Consul Connect's built-in proxy for this guide. In a
production deployment, we recommend using Envoy instead.

```shell-session
$ consul connect proxy -sidecar-for counting > counting-proxy.log &
$ consul connect proxy -sidecar-for dashboard > dashboard-proxy.log &
```

### Check the dashboard interface

Open a browser and navigate to `http://localhost:9002`.

You should see a screen similar to the following. There is a connection
indicator in the top right that will turn green and say "Connected" when the
dashboard service is in communication with the counting service.

[![Image of Dashboard UI. There is white text on a magenta background, with the
page title "Dashboard" at the top left. There is a green indicator in the top
right with the word connected in white.  There is a large number 19 to show
sample counting output. The node name that the counting service is running on,
host01, is in very small monospaced type underneath the large
numbers.][img-screenshot1]][img-screenshot1]

If your application is not connected, check that the Counting service is
running and healthy by viewing it in the Consul UI at `http://localhost:8500`.

## Test the sidecar proxy connections

To test that traffic is flowing through the sidecar proxies, you will control
traffic with an intention.

First, deny the Dashboard service access to the Counting service.

```shell-session
$ consul intention create -deny -replace dashboard counting
Created: dashboard => counting (deny)
```

Refresh your browser, the connection indicator in the Dashboard ui will now say
"Disconnected"

[![Image of Dashboard UI. There is white text on a magenta background, with the
page title "Dashboard" at the top left. There is a red indicator in the top
right with the words "Counting Service is Unreachable" in white.  There is a
large number -1 to show sample counting output. The word "Unreachable"
surrounded by square brackets is in monospaced type underneath the large
numbers.][img-screenshot2]][img-screenshot2]

You can restore communication between the services by replacing the `deny`
intention with an `allow`.

```shell-session
$ consul intention create -allow -replace dashboard counting
```

Back in the browser, verify that the dashboard reconnects to the counting
service.

## Clean up

Once you are done with this guide, you can begin cleaning up by closing the
terminal in which your counting-service, dashboard-service, and proxies are
running. This should automatically stop these processes.

Delete the intention from Consul.

```shell-session
$ consul intention delete dashboard counting
Intention deleted.
```

Deregister the services.

```shell-session
$ consul services deregister counting.hcl
Deregistered service: counting

$ consul services deregister dashboard.hcl
Deregistered service: dashboard
```

## Extend these concepts

When you want to apply this learning to a proof-of-concept or production
environment, there are some additional considerations.

### Enable Connect and gRPC

When Consul is started with the `-dev` flag, it will automatically enable
Consul Connect and provide a default port for gRPC communication. These have to
be configured explicitly for regular Consul agents.

```hcl
# ...

ports {
  "grpc" = 8502
}

connect {
  enabled = true
}

```

For JSON configurations:

```json
{
  // ...
  "ports": {
    "grpc": 8502
  },
  "connect": {
    "enabled": true
  }
}
```

### Download Envoy

In this guide we used the built-in Connect proxy. For production deployments
and to enable L7 features, you should use Envoy.

You can obtain container-based builds of Envoy directly from the [Envoy
Website], or you can obtain a packages of Envoy binary builds from a
third-party project, [getenvoy.io].

Consul will need to be able to find the "envoy" binary on the path. You can
extract the binary from the official Envoy Docker containers.

To do this, create a container named "envoy-extract" based on the
"envoyproxy/envoy" container.

```shell-session
$ docker create --name "envoy-extract" "envoyproxy/envoy"
docker create --name "envoy-extract" "envoyproxy/envoy"
Unable to find image 'envoyproxy/envoy:latest' locally
latest: Pulling from envoyproxy/envoy
16c48d79e9cc: Pull complete
3c654ad3ed7d: Pull complete
6276f4f9c29d: Pull complete
a4bd43ad48ce: Pull complete
ef9506777d3e: Pull complete
2e7ad8d4ceb7: Pull complete
d9e379d45dad: Pull complete
b283a3f5aebc: Pull complete
095fe71f6465: Pull complete
Digest: sha256:a7769160c9c1a55bb8d07a3b71ce5d64f72b1f665f10d81aa1581bc3cf850d09
Status: Downloaded newer image for envoyproxy/envoy:latest
8d7bb45ea75f4344c6e050e5e1d3423937c4a1a51700ce34c3cf62a5ce3960dd
```

Use the `docker cp` command to copy the envoy file out of the container into
the current directory.

```shell-session
$ docker cp "envoy-extract:/usr/local/bin/envoy" "envoy"
```

Now that you have the binary, you can remove the "envoy-extract" container.

```shell-session
$ docker rm "envoy-extract"
envoy-extract
```

Once you have the binary extracted and in your path, Consul will automatically
use it when you run the `consul connect envoy` command. The following examples
demonstrate how to start the service sidecar proxies with Envoy.

```shell-session
$ consul connect envoy -sidecar-for counting > counting-proxy.log &
$ consul connect envoy -sidecar-for dashboard > dashboard-proxy.log &
```

## Summary

Now that you have completed this guide, you have familiarized yourself with a
basic Connect-enabled service deployment. You created and registered Consul
service definitions that describe how two services communicate with each other.
After starting the application and sidecar proxies, you used Consul Connect
intentions to control traffic flow between services. Finally, you learned about
additional requirements required to take the concepts to a proof-of-concept
environment.

[connect]: https://www.consul.io/docs/connect
[consul-l7]: https://learn.hashicorp.com/consul/developer-mesh/l7-observability-k8s
[counting service]: https://github.com/hashicorp/demo-consul-101/releases/download/0.0.2/counting-service_linux_amd64.zip
[counting-1.json]: https://raw.githubusercontent.com/hashicorp/demo-consul-101/master/demo-config-localhost/counting-1.json
[dashboard service]: https://github.com/hashicorp/demo-consul-101/releases/download/0.0.2/dashboard-service_linux_amd64.zip
[dashboard.json]: https://raw.githubusercontent.com/hashicorp/demo-consul-101/master/demo-config-localhost/dashboard.json
[default acl policy]: https://www.consul.io/docs/agent/options#acl_default_policy
[demo-consul-101 project]: https://github.com/hashicorp/demo-consul-101
[dev agent]: https://learn.hashicorp.com/consul/getting-started/agent
[docker guide]: https://learn.hashicorp.com/consul/day-0/containers-guide
[envoy website]: https://www.envoyproxy.io/docs/envoy/latest/install/building#pre-built-binaries
[getenvoy.io]: https://www.getenvoy.io/
[img-flow]: /static/img/consul/connect-getting-started/consul_connect_demo_service_flow.png
[img-screenshot1]: /static/img/consul/connect-getting-started/screenshot1.png
[img-screenshot2]: /static/img/consul/connect-getting-started/screenshot2.png
[intention]: https://www.consul.io/docs/connect/intentions
[services-api]: https://www.consul.io/api/agent/service#register-service
[services-cli]: https://www.consul.io/docs/commands/services
[services-config]: https://www.consul.io/docs/agent/services#service-definition
[services-nomad]: https://www.nomadproject.io/docs/job-specification/service
[sidecar]: https://docs.microsoft.com/en-us/azure/architecture/patterns/sidecar
[sidecar_service]: https://www.consul.io/docs/connect/registration/sidecar-service
[services-k8s]: https://www.consul.io/docs/platform/k8s/connect#installation-and-configuration