---
layout: docs
page_title: Service Mesh - Kubernetes
description: >-
  Connect is a feature built into to Consul that enables automatic
  service-to-service authorization and connection encryption across your Consul
  services. Connect can be used with Kubernetes to secure pod communication with
  other services.
---

# Connect Service Mesh on Kubernetes

[Connect](/docs/connect) is a feature built into to Consul that enables
automatic service-to-service authorization and connection encryption across
your Consul services. Connect can be used with Kubernetes to secure pod
communication with other pods and external Kubernetes services.

The Connect sidecar running Envoy can be automatically injected into pods in
your cluster, making configuration for Kubernetes automatic.
This functionality is provided by the
[consul-k8s project](https://github.com/hashicorp/consul-k8s) and can be
automatically installed and configured using the
[Consul Helm chart](/docs/k8s/installation/install).

## Usage

When the
[Connect injector is installed](/docs/k8s/connect#installation-and-configuration),
the Connect sidecar can be automatically added to all pods. This sidecar can both
accept and establish connections using Connect, enabling the pod to communicate
to clients and dependencies exclusively over authorized and encrypted
connections.

-> **Note:** The examples in this section are valid and use
publicly available images. If you've installed the Connect injector, feel free
to run the examples in this section to try Connect with Kubernetes.
Please note the documentation below this section on how to properly install
and configure the Connect injector.

### Accepting Inbound Connections

An example Deployment is shown below with Connect enabled to accept inbound
connections. Notice that the Deployment would still be fully functional without
Connect. Minimal to zero modifications are required to enable Connect in Kubernetes.
Notice also that even though we're using a Deployment here, the same configuration
would work on a Pod, a StatefulSet, or a DaemonSet.

This Deployment specification starts a server that responds to any
HTTP request with the static text "hello world".

-> **Note:** As of consul-k8s `v0.26.0` and Consul Helm `v0.32.0`, having a Kubernetes
service is **required** to run services on the Consul Service Mesh.

```yaml
apiVersion: v1
kind: Service
metadata:
  # This name will be the service name in Consul.
  name: static-server
spec:
  selector:
    app: static-server
  ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-server
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-server
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-server
  template:
    metadata:
      name: static-server
      labels:
        app: static-server
      annotations:
        'consul.hashicorp.com/connect-inject': 'true'
    spec:
      containers:
        - name: static-server
          image: hashicorp/http-echo:latest
          args:
            - -text="hello world"
            - -listen=:8080
          ports:
            - containerPort: 8080
              name: http
      # If ACLs are enabled, the serviceAccountName must match the Consul service name.
      serviceAccountName: static-server
```

The only change for Connect is the addition of the
`consul.hashicorp.com/connect-inject` annotation. This enables injection
for the Pod in this Deployment. The injector can also be
[configured](/docs/k8s/connect#installation-and-configuration)
to automatically inject unless explicitly disabled, but the default
installation requires opt-in using the annotation shown above.

~> **A common mistake** is to set the annotation on the Deployment or
other resource. Ensure that the injector annotations are specified on
the _pod specification template_ as shown above.

This will start a sidecar proxy that listens on port `20000` registered
with Consul and proxies valid inbound connections to port 8080 in the pod.
To establish a connection to the pod using Connect, a client must use another Connect
proxy. The client Connect proxy will use Consul service discovery to find
all available upstream proxies and their public ports.

In the example above, the server is listening on `:8080`.
By default, the Consul Service Mesh runs in [transparent proxy](/docs/connect/transparent-proxy) mode.
This means that even though the server binds to all interfaces,
the inbound and outbound connections will automatically go through to the sidecar proxy.
It also allows you to use Kubernetes DNS like you normally would without the
Consul Service Mesh.

-> **Note:** As of consul `v1.10.0`, consul-k8s `v0.26.0` and Consul Helm `v0.32.0`,
all Consul Service Mesh services will run with transparent proxy enabled by default. Running with transparent
proxy will enforce all inbound and outbound traffic to go through the Envoy proxy.

The service name registered in Consul will be set to the name of the Kubernetes service
associated with the Pod. This can be customized with the `consul.hashicorp.com/connect-service`
annotation. If using ACLs, this name must be the same as the Pod's `ServiceAccount` name.

### Connecting to Connect-Enabled Services

The example Deployment specification below configures a Deployment that is capable
of establishing connections to our previous example "static-server" service. The
connection to this static text service happens over an authorized and encrypted
connection via Connect.

-> **Note:** As of consul-k8s `v0.26.0` and Consul Helm `v0.32.0`, having a Kubernetes
Service is **required** to run services on the Consul Service Mesh.

```yaml
apiVersion: v1
kind: Service
metadata:
  # This name will be the service name in Consul.
  name: static-client
spec:
  selector:
    app: static-client
  ports:
    - port: 80
---
apiVersion: v1
kind: ServiceAccount
metadata:
  name: static-client
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: static-client
spec:
  replicas: 1
  selector:
    matchLabels:
      app: static-client
  template:
    metadata:
      name: static-client
      labels:
        app: static-client
      annotations:
        'consul.hashicorp.com/connect-inject': 'true'
    spec:
      containers:
        - name: static-client
          image: curlimages/curl:latest
          # Just spin & wait forever, we'll use `kubectl exec` to demo
          command: ['/bin/sh', '-c', '--']
          args: ['while true; do sleep 30; done;']
      # If ACLs are enabled, the serviceAccountName must match the Consul service name.
      serviceAccountName: static-client
```

By default when ACLs are enabled or when ACLs default policy is `allow`,
Consul will automatically configure proxies with all upstreams from the same datacenter.
When ACLs are enabled with default `deny` policy,
you must supply an [intention](/docs/connect/intentions) to tell Consul which upstream you need to talk to.

When upstreams are specified explicitly with the
[`consul.hashicorp.com/connect-service-upstreams` annotation](/docs/k8s/connect#consul-hashicorp-com-connect-service-upstreams),
the injector will also set environment variables `<NAME>_CONNECT_SERVICE_HOST`
and `<NAME>_CONNECT_SERVICE_PORT` in every container in the Pod for every defined
upstream. This is analogous to the standard Kubernetes service environment variables, but
point instead to the correct local proxy port to establish connections via
Connect.

We can verify access to the static text server using `kubectl exec`.
Because transparent proxy is enabled by default,
we use Kubernetes DNS to connect to our desired upstream.

```shell-session
$ kubectl exec deploy/static-client -- curl --silent http://static-server/
"hello world"
```

We can control access to the server using [intentions](/docs/connect/intentions).
If you use the Consul UI or [CLI](/commands/intention/create) to
create a deny [intention](/docs/connect/intentions) between
"static-client" and "static-server", connections are immediately rejected
without updating either of the running pods. You can then remove this
intention to allow connections again.

```shell-session
$ kubectl exec deploy/static-client -- curl --silent http://static-server/
command terminated with exit code 52
```

## Installation and Configuration

The Connect sidecar proxy is injected via a
[mutating admission webhook](https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks)
provided by the
[consul-k8s project](https://github.com/hashicorp/consul-k8s).
This enables the automatic pod mutation shown in the usage section above.
Installation of the mutating admission webhook is automated using the
[Helm chart](/docs/k8s/installation/install).

To install the Connect injector, enable the Connect injection feature using
[Helm values](/docs/k8s/helm#configuration-values) and
upgrade the installation using `helm upgrade` for existing installs or
`helm install` for a fresh install.

```yaml
connectInject:
  enabled: true

controller:
  enabled: true
```

This will configure the injector to inject when the
[injection annotation](#consul-hashicorp-com-connect-inject)
is set to `true`. Other values in the Helm chart can be used to limit the namespaces
the injector runs in, enable injection by default, and more.

### Controlling Injection Via Annotation

By default, the injector will inject only when the
[injection annotation](#consul-hashicorp-com-connect-inject)
on the pod (not the deployment) is set to `true`:

```yaml
annotations:
  'consul.hashicorp.com/connect-inject': 'true'
```

### Injection Defaults

If you wish for the injector to always inject, you can set the default to `true`
in the Helm chart:

```yaml
connectInject:
  enabled: true
  default: true
```

You can then exclude specific pods via annotation:

```yaml
annotations:
  'consul.hashicorp.com/connect-inject': 'false'
```

### Controlling Injection Via Namespace

You can control which Kubernetes namespaces are allowed to be injected via
the `k8sAllowNamespaces` and `k8sDenyNamespaces` keys:

```yaml
connectInject:
  enabled: true
  k8sAllowNamespaces: ['*']
  k8sDenyNamespaces: []
```

In the default configuration (shown above), services from all namespaces are allowed
to be injected. Whether or not they're injected depends on the value of `connectInject.default`
and the `consul.hashicorp.com/connect-inject` annotation.

If you wish to only enable injection in specific namespaces, you can list only those
namespaces in the `k8sAllowNamespaces` key. In the configuration below
only the `my-ns-1` and `my-ns-2` namespaces will be enabled for injection.
All other namespaces will be ignored, even if the connect inject [annotation](#consul-hashicorp-com-connect-inject)
is set.

```yaml
connectInject:
  enabled: true
  k8sAllowNamespaces: ['my-ns-1', 'my-ns-2']
  k8sDenyNamespaces: []
```

If you wish to enable injection in every namespace _except_ specific namespaces, you can
use `*` in the allow list to allow all namespaces and then specify the namespaces to exclude in the deny list:

```yaml
connectInject:
  enabled: true
  k8sAllowNamespaces: ['*']
  k8sDenyNamespaces: ['no-inject-ns-1', 'no-inject-ns-2']
```

-> **NOTE:** The deny list takes precedence over the allow list. If a namespace
is listed in both lists, it will **not** be synced.

~> **NOTE:** The `kube-system` and `kube-public` namespaces will never be injected.

### Consul Enterprise Namespaces

Consul Enterprise 1.7+ supports Consul namespaces. When Kubernetes pods are registered
into Consul, you can control which Consul namespace they are registered into.

There are three options available:

1.  **Single Destination Namespace** – Register all Kubernetes pods, regardless of namespace,
    into the same Consul namespace.

    This can be configured with:

    ```yaml
    global:
      enableConsulNamespaces: true

    connectInject:
      enabled: true
      consulNamespaces:
        consulDestinationNamespace: 'my-consul-ns'
    ```

    -> **NOTE:** If the destination namespace does not exist we will create it.

1.  **Mirror Namespaces** - Register each Kubernetes pod into a Consul namespace with the same name as its Kubernetes namespace.
    For example, pod `foo` in Kubernetes namespace `ns-1` will be synced to the Consul namespace `ns-1`.
    If a mirrored namespace does not exist in Consul, it will be created.

    This can be configured with:

    ```yaml
    global:
      enableConsulNamespaces: true

    connectInject:
      enabled: true
      consulNamespaces:
        mirroringK8S: true
    ```

1.  **Mirror Namespaces With Prefix** - Register each Kubernetes pod into a Consul namespace with the same name as its Kubernetes
    namespace **with a prefix**.
    For example, given a prefix `k8s-`, pod `foo` in Kubernetes namespace `ns-1` will be synced to the Consul namespace `k8s-ns-1`.

    This can be configured with:

    ```yaml
    global:
      enableConsulNamespaces: true

    connectInject:
      enabled: true
      consulNamespaces:
        mirroringK8S: true
        mirroringK8SPrefix: 'k8s-'
    ```

### Consul Enterprise Namespace Upstreams

When [transparent proxy](/docs/connect/transparent-proxy) is enabled and ACLs are disabled,
the upstreams will be configured automatically across Consul namespaces.
When ACLs are enabled, you must configure it by specifying an [intention](/docs/connect/intentions),
allowing services across Consul namespaces to talk to each other.

If you wish to specify an upstream explicitly via the `consul.hashicorp.com/connect-service-upstreams` annotation,
use the format `[service-name].[namespace]:[port]:[optional datacenter]`:

```yaml
annotations:
  'consul.hashicorp.com/connect-inject': 'true'
  'consul.hashicorp.com/connect-service-upstreams': '[service-name].[namespace]:[port]:[optional datacenter]'
```

See [consul.hashicorp.com/connect-service-upstreams](#consul-hashicorp-com-connect-service-upstreams) for more details.

-> **Note:** When you specify upstreams via an upstreams annotation, you will need to use
`localhost:<port>` with the port from the upstreams annotation instead of KubeDNS to connect to your upstream
application.

### Verifying the Installation

To verify the installation, run the
["Accepting Inbound Connections"](/docs/k8s/connect#accepting-inbound-connections)
example from the "Usage" section above. After running this example, run
`kubectl get pod static-server --output yaml`. In the raw YAML output, you should
see injected Connect containers and an annotation
`consul.hashicorp.com/connect-inject-status` set to `injected`. This
confirms that injection is working properly.

If you do not see this, then use `kubectl logs` against the injector pod
and note any errors.
