»Connect Service Mesh on Kubernetes
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 and can be automatically installed and configured using the Consul Helm chart.
When the Connect injector is installed, 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 pod specifications in this section are valid and use publicly available images. If you've installed the Connect injector, feel free to run the pod specifications 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 pod is shown below with Connect enabled to accept inbound connections. Notice that the pod would still be fully functional without Connect. Minimal to zero modifications are required to pod specifications to enable Connect in Kubernetes.
This pod specification starts a server that responds to any HTTP request with the static text "hello world".
apiVersion: v1 kind: ServiceAccount metadata: name: static-server --- apiVersion: v1 kind: Pod metadata: name: static-server annotations: 'consul.hashicorp.com/connect-inject': 'true' spec: containers: # This name will be the service name in Consul. - 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 this pod. The injector can also be
to automatically inject unless explicitly disabled, but the default
installation requires opt-in using the annotation shown above.
This will start a Connect sidecar that listens on a random port 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. This means
the server will still bind to the pod IP and allow external connections.
This is useful to transition to Connect by allowing both Connect and
non-Connect connections. To restrict access to only Connect-authorized clients,
any listeners should bind to localhost only (such as
The service name registered in Consul will be set to the name of the first
container in the Pod. This can be customized with the
annotation. If using ACLs, this name must be the same as the Pod's
»Connecting to Connect-Enabled Services
The example pod specification below configures a pod 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.
apiVersion: v1 kind: ServiceAccount metadata: name: static-client --- apiVersion: v1 kind: Pod metadata: name: static-client annotations: 'consul.hashicorp.com/connect-inject': 'true' 'consul.hashicorp.com/connect-service-upstreams': 'static-server:1234' spec: containers: # This name will be the service name in Consul. - name: static-client image: tutum/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
Pods must specify upstream dependencies with the
This annotation declares the names of any upstream dependencies and a
local port for the proxy to listen on. When a connection is established to that local
port, the proxy establishes a connection to the target service
static-server in this example) using
mutual TLS and identifying as the source service (
static-client in this
The injector will also set environment variables
<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
Any containers running in the pod that need to establish connections to dependencies must be reconfigured to use the local upstream address either directly or using the environment variables set by the injector (defined above). This means pods should not use Kubernetes service DNS or environment variables for these connections.
We can verify access to the static text server using
kubectl exec. Notice
that we use the local address and port from the upstream annotation (1234)
for this verification.
$ kubectl exec static-client -- curl -s http://127.0.0.1:1234/ "hello world"
We can control access to the server using intentions. If you use the Consul UI or CLI to create a deny intention 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.
$ kubectl exec static-client -- curl -s http://127.0.0.1:1234/ command terminated with exit code 52
Annotations can be used to configure the injection behavior.
consul.hashicorp.com/connect-inject- If this is "true" then injection is enabled. If this is "false" then injection is explicitly disabled. The default injector behavior requires pods to opt-in to injection by specifying this value as "true". This default can be changed in the injector's configuration if desired.
consul.hashicorp.com/connect-service- For pods that accept inbound connections, this specifies the name of the service that is being served. This defaults to the name of the first container in the pod.
If using ACLs, this must be the same name as the Pod's
consul.hashicorp.com/connect-service-port- For pods that accept inbound connections, this specifies the port to route inbound connections to. This is the port that the service is listening on. The service port defaults to the first exposed port on any container in the pod. If specified, the value can be the name of a configured port, such as "http" or it can be a direct port value such as "8080". This is the port of the service, the proxy public listener will listen on a dynamic port.
consul.hashicorp.com/connect-service-upstreams- The list of upstream services that this pod needs to connect to via Connect along with a static local port to listen for those connections.
The name of the service is the name of the service registered with Consul. You can optionally specify datacenters with this annotation.
annotations: "consul.hashicorp.com/connect-service-upstreams":"[service-name]:[port]:[optional datacenter]"
Consul Enterprise Namespaces
If running Consul Enterprise 1.7+, your upstream services may be running in different namespaces. The upstream namespace can be specified after the service name as
[service-name].[namespace]. See Consul Enterprise Namespaces below for more details on configuring the injector.
annotations: "consul.hashicorp.com/connect-service-upstreams":"[service-name].[service-namespace]:[port]:[optional datacenter]"
NOTE: If the namespace is not specified it will default to the namespace of the source service.
WARNING: Setting a namespace when not using Consul Enterprise or using a version < 1.7 is not supported. It will be treated as part of the service name.
annotations: 'consul.hashicorp.com/connect-service-upstreams': 'prepared_query:[query name]:[port]'
If you would like to specify multiple services or upstreams, delimit them with commas
annotations: "consul.hashicorp.com/connect-service-upstreams":"[service-name]:[port]:[optional datacenter],[service-name]:[port]:[optional datacenter]"
annotations: "consul.hashicorp.com/connect-service-upstreams":"[service-name]:[port]:[optional datacenter],prepared_query:[query name]:[port]"
consul.hashicorp.com/connect-service-protocol- For pods that will be registered with Consul's central configuration feature, information about the protocol the service uses is required. Users can define the protocol directly using this annotation on the pod spec, or by defining a default value for all services using the Helm chart's defaultProtocol option. Specific annotations will always override the default value.
consul.hashicorp.com/service-tags- A comma separated list of tags that will be applied to the Consul service and its sidecar.
annotations: consul.hashicorp.com/service-tags: foo,bar,baz
consul.hashicorp.com/service-meta-<YOUR_KEY>- Set Consul meta key/value pairs that will be applied to the Consul service and its sidecar. The key will be what comes after
consul.hashicorp.com/service-meta-foo: barwill result in
annotations: consul.hashicorp.com/service-meta-foo: baz consul.hashicorp.com/service-meta-bar: baz
»Deployments, StatefulSets, etc.
The annotations for configuring Connect must be on the pod specification. Since higher level resources such as Deployments wrap pod specification templates, Connect can be used with all of these higher level constructs, too.
Deployment below shows how to enable Connect injection:
apiVersion: apps/v1 kind: Deployment metadata: name: consul-example-deployment spec: replicas: 1 selector: matchLabels: app: consul-example template: metadata: labels: app: consul-example annotations: 'consul.hashicorp.com/connect-inject': 'true' spec: containers: - name: consul-example image: 'nginx' serviceAccountName: consul-example --- apiVersion: v1 kind: ServiceAccount metadata: name: consul-example
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.
»Installation and Configuration
The Connect sidecar proxy is injected via a mutating admission webhook provided by the consul-k8s project. This enables the automatic pod mutation shown in the usage section above. Installation of the mutating admission webhook is automated using the Helm chart.
To install the Connect injector, enable the Connect injection feature using
Helm values and
upgrade the installation using
helm upgrade for existing installs or
helm install for a fresh install. The Connect injector also requires
client agents are enabled on
the node with pods that are using Connect and that
gRPC is enabled.
connectInject: enabled: true client: enabled: true
This will configure the injector to inject when the
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.
NOTE: If setting
global.bootstrapACLs: true, it's important that your pod's
has the same name as the Consul service that's being registered. If not, the init
container will log:
Error logging in: Unexpected response code: 403 (rpc error making call: rpc error making call: Permission denied).
»Controlling Injection Via Annotation
By default, the injector will inject only when the
on the pod (not the deployment) is set to
annotations: 'consul.hashicorp.com/connect-inject': 'true'
If you wish for the injector to always inject, you can set the default to
in the Helm chart:
connectInject: enabled: true default: true
You can then exclude specific pods via annotation:
annotations: 'consul.hashicorp.com/connect-inject': 'false'
»Controlling Injection Via Namespace
You can control which Kubernetes namespaces are allowed to be injected via
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
If you wish to only enable injection in specific namespaces, you can list only those
namespaces in the
k8sAllowNamespaces key. In the configuration below
my-ns-2 namespaces will be enabled for injection.
All other namespaces will be ignored, even if the connect inject annotation
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
* in the allow list to allow all namespaces and then specify the namespaces to exclude in the deny list:
syncCatalog: enabled: true k8sAllowNamespaces: ['*'] k8sDenyNamespaces: ['no-sync-ns-1', 'no-sync-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.
kube-public namespaces will never be injected.
»Consul Clients Required
Connect injection requires that local client agents are running on each Kubernetes node. These client agents must be joined to a Consul server cluster. The Consul server cluster can run either in or out of a Kubernetes cluster.
»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:
Single Destination Namespace – Register all Kubernetes pods, regardless of namespace, into the same Consul namespace.
This can be configured with:
global: enableConsulNamespaces: true connectInject: enabled: true consulNamespaces: consulDestinationNamespace: 'my-consul-ns'
NOTE: If the destination namespace does not exist we will create it.
Mirror Namespaces - Register each Kubernetes pod into a Consul namespace with the same name as its Kubernetes namespace. For example, pod
fooin Kubernetes namespace
ns-1will 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:
global: enableConsulNamespaces: true connectInject: enabled: true consulNamespaces: mirroringK8S: true
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
fooin Kubernetes namespace
ns-1will be synced to the Consul namespace
This can be configured with:
global: enableConsulNamespaces: true connectInject: enabled: true consulNamespaces: mirroringK8S: true mirroringK8SPrefix: 'k8s-'
»Consul Enterprise Namespace Upstreams
To specify the namespace of your upstream services in the upstream annotation,
use the format
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 for more details.
»Verifying the Installation
To verify the installation, run the
"Accepting Inbound Connections"
example from the "Usage" section above. After running this example, run
kubectl get pod static-server -o yaml. In the raw YAML output, you should
see injected Connect containers and an annotation
consul.hashicorp.com/connect-inject-status set to
confirms that injection is working properly.
If you do not see this, then use
kubectl logs against the injector pod
and note any errors.