--- layout: docs page_title: How does Consul Service Mesh Work on Kubernetes? description: >- An injection annotation allows Consul to automatically deploy sidecar proxies on Kubernetes pods, enabling Consul's service mesh for containers running on k8s. Learn how to configure sidecars, enable services with multiple ports, change default injection settings. --- # How does Consul Service Mesh Work on Kubernetes? Consul service mesh automates service-to-service authorization and encryption across your Consul services. You can use service mesh in Kubernetes-orchestrated networks to secure communication between pods as well as communication between pods and external Kubernetes services. ## Workflow Consul service mesh is enabled by default when you install Consul on Kubernetes using the Consul Helm chart. Consul also automatically injects sidecars into the pods in your clusters that run Envoy. These sidecar proxies, called Consul dataplanes, are enabled when `connectInject.default` is set to `false` in the Helm chart. Refer to the following documentation for additional information about these concepts: - [Installation and Configuration](#installation-and-configuration) in this topic - [Consul Helm chart reference](/consul/docs/k8s/helm) - [Simplified Service Mesh with Consul Dataplane](/consul/docs/connect/dataplane) If `connectInject.default` is set to `false` or you want to explicitly enable service mesh sidecar proxy injection for a specific deployment, add the `consul.hashicorp.com/connect-inject` annotation to the pod specification template and set it to `true` when connecting services to the mesh. ### Service names When the service is onboarded, the name registered in Consul is set to the name of the Kubernetes Service associated with the Pod. You can use the [`consul.hashicorp.com/connect-service` annotation](/consul/docs/k8s/annotations-and-labels#consul-hashicorp-com-connect-service) to specify a custom name for the service, but if ACLs are enabled then the name of the service registered in Consul must match the Pod's `ServiceAccount` name. ### Transparent proxy mode By default, the Consul service mesh runs in transparent proxy mode. This mode forces inbound and outbound traffic through the sidecar proxy even though the service binds to all interfaces. Transparent proxy infers the location of upstream services using Consul service intentions, and also allows you to use Kubernetes DNS as you normally would for your workloads. When transparent proxy mode is enabled, all service-to-service traffic is required to use mTLS. When onboarding new services to service mesh, your network may have mixed mTLS and non-mTLS traffic, which can result in broken service-to-service communication. You can temporarily enable permissive mTLS mode during the onboarding process so that existing mesh services can accept traffic from services that are not yet fully onboarded. Permissive mTLS enables sidecar proxies to access both mTLS and non-mTLS traffic. Refer to [Onboard mesh services in transparent proxy mode](/consul/docs/k8s/connect/onboarding-tproxy-mode) for additional information. ### Kubernetes service mesh workload scenarios -> **Note:** A Kubernetes Service is required in order to register services on the Consul service mesh. Consul monitors the lifecycle of the Kubernetes Service and its service instances using the service object. In addition, the Kubernetes service is used to register and de-register the service from Consul's catalog. The following configurations are examples for registering workloads on Kubernetes into Consul's service mesh in different scenarios. Each scenario provides an example Kubernetes manifest to demonstrate how to use Consul's service mesh with a specific Kubernetes workload type. - [Kubernetes Pods running as a deployment](#kubernetes-pods-running-as-a-deployment) - [Connecting to mesh-enabled Services](#connecting-to-mesh-enabled-services) - [Kubernetes Jobs](#kubernetes-jobs) - [Kubernetes Pods with multiple ports](#kubernetes-pods-with-multiple-ports) #### Kubernetes Pods running as a deployment The following example shows a Kubernetes configuration that specifically enables service mesh connections for the `static-server` service. Consul starts and registers a sidecar proxy that listens on port 20000 by default and proxies valid inbound connections to port 8080. ```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 ``` To establish a connection to the upstream Pod using service mesh, a client must dial the upstream workload using a mesh proxy. The client mesh proxy will use Consul service discovery to find all available upstream proxies and their public ports. #### Connecting to mesh-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 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](/consul/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](/consul/docs/k8s/annotations-and-labels#consul-hashicorp-com-connect-service-upstreams), the injector will also set environment variables `_CONNECT_SERVICE_HOST` and `_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 service mesh. You cannot reference auto-generated environment variables when the upstream annotation contains a dot. This is because Consul also renders the environment variables to include a dot. For example, Consul renders the variables generated for `static-server.svc:8080` as `STATIC-SERVER.SVC_CONNECT_SERVICE_HOST` and `STATIC_SERVER.SVC_CONNECT_SERVICE_PORT`, which makes the variables unusable. You can verify access to the static text server using `kubectl exec`. Because transparent proxy is enabled by default, use Kubernetes DNS to connect to your desired upstream. ```shell-session $ kubectl exec deploy/static-client -- curl --silent http://static-server/ "hello world" ``` You can control access to the server using [intentions](/consul/docs/connect/intentions). If you use the Consul UI or [CLI](/consul/commands/intention/create) to deny communication 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 ``` #### Kubernetes Jobs Kubernetes Jobs run pods that only make outbound requests to services on the mesh and successfully terminate when they are complete. In order to register a Kubernetes Job with the mesh, you must provide an integer value for the `consul.hashicorp.com/sidecar-proxy-lifecycle-shutdown-grace-period-seconds` annotation. Then, issue a request to the `http://127.0.0.1:20600/graceful_shutdown` API endpoint so that Kubernetes gracefully shuts down the `consul-dataplane` sidecar after the job is complete. Below is an example Kubernetes manifest that deploys a job correctly. ```yaml --- apiVersion: v1 kind: ServiceAccount metadata: name: test-job namespace: default --- apiVersion: v1 kind: Service metadata: name: test-job namespace: default spec: selector: app: test-job ports: - port: 80 --- apiVersion: batch/v1 kind: Job metadata: name: test-job namespace: default labels: app: test-job spec: template: metadata: annotations: 'consul.hashicorp.com/connect-inject': 'true' 'consul.hashicorp.com/sidecar-proxy-lifecycle-shutdown-grace-period-seconds': '5' labels: app: test-job spec: containers: - name: test-job image: alpine/curl:3.14 ports: - containerPort: 80 command: - /bin/sh - -c - | echo "Started test job" sleep 10 echo "Killing proxy" curl --max-time 2 -s -f -X POST http://127.0.0.1:20600/graceful_shutdown sleep 10 echo "Ended test job" serviceAccountName: test-job restartPolicy: Never ``` Upon completing the job you should be able to verify that all containers are shut down within the pod. ```shell-session $ kubectl get pods NAME READY STATUS RESTARTS AGE test-job-49st7 0/2 Completed 0 3m55s ``` ```shell-session $ kubectl get job NAME COMPLETIONS DURATION AGE test-job 1/1 30s 4m31s ``` In addition, based on the logs emitted by the pod you can verify that the proxy was shut down before the Job completed. ```shell-session $ kubectl logs test-job-49st7 -c test-job Started test job Killing proxy Ended test job ``` #### Kubernetes Pods with multiple ports To configure a pod with multiple ports to be a part of the service mesh and receive and send service mesh traffic, you will need to add configuration so that a Consul service can be registered per port. This is because services in Consul currently support a single port per service instance. In the following example, suppose we have a pod which exposes 2 ports, `8080` and `9090`, both of which will need to receive service mesh traffic. First, decide on the names for the two Consul services that will correspond to those ports. In this example, the user chooses the names `web` for `8080` and `web-admin` for `9090`. Create two service accounts for `web` and `web-admin`: ```yaml apiVersion: v1 kind: ServiceAccount metadata: name: web --- apiVersion: v1 kind: ServiceAccount metadata: name: web-admin ``` Create two Service objects for `web` and `web-admin`: ```yaml apiVersion: v1 kind: Service metadata: name: web spec: selector: app: web ports: - protocol: TCP port: 80 targetPort: 8080 --- apiVersion: v1 kind: Service metadata: name: web-admin spec: selector: app: web ports: - protocol: TCP port: 80 targetPort: 9090 ``` `web` will target `containerPort` `8080` and select pods labeled `app: web`. `web-admin` will target `containerPort` `9090` and will also select the same pods. ~> Kubernetes 1.24+ only In Kubernetes 1.24+ you need to [create a Kubernetes secret](https://kubernetes.io/docs/concepts/configuration/secret/#service-account-token-secrets) for each additional Consul service associated with the pod in order to expose the Kubernetes ServiceAccount token to the Consul dataplane container running under the pod serviceAccount. The Kubernetes secret name must match the ServiceAccount name: ```yaml apiVersion: v1 kind: Secret metadata: name: web annotations: kubernetes.io/service-account.name: web type: kubernetes.io/service-account-token --- apiVersion: v1 kind: Secret metadata: name: web-admin annotations: kubernetes.io/service-account.name: web-admin type: kubernetes.io/service-account-token ``` Create a Deployment with any chosen name, and use the following annotations: ```yaml annotations: 'consul.hashicorp.com/connect-inject': 'true' 'consul.hashicorp.com/transparent-proxy': 'false' 'consul.hashicorp.com/connect-service': 'web,web-admin' 'consul.hashicorp.com/connect-service-port': '8080,9090' ``` Note that the order the ports are listed in the same order as the service names, i.e. the first service name `web` corresponds to the first port, `8080`, and the second service name `web-admin` corresponds to the second port, `9090`. The service account on the pod spec for the deployment should be set to the first service name `web`: ```yaml serviceAccountName: web ``` The following deployment example demonstrates the required annotations for the manifest. In addition, the previous YAML manifests can also be combined into a single manifest for easier deployment. ```yaml apiVersion: apps/v1 kind: Deployment metadata: name: web spec: replicas: 1 selector: matchLabels: app: web template: metadata: name: web labels: app: web annotations: 'consul.hashicorp.com/connect-inject': 'true' 'consul.hashicorp.com/transparent-proxy': 'false' 'consul.hashicorp.com/connect-service': 'web,web-admin' 'consul.hashicorp.com/connect-service-port': '8080,9090' spec: containers: - name: web image: hashicorp/http-echo:latest args: - -text="hello world" - -listen=:8080 ports: - containerPort: 8080 name: http - name: web-admin image: hashicorp/http-echo:latest args: - -text="hello world from 9090" - -listen=:9090 ports: - containerPort: 9090 name: http serviceAccountName: web ``` After deploying the `web` application, you can test service mesh connections by deploying the `static-client` application with the configuration in the [previous section](#connecting-to-mesh-enabled-services) and add the `consul.hashicorp.com/connect-service-upstreams: 'web:1234,web-admin:2234'` annotation to the pod template on `static-client`: ```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' 'consul.hashicorp.com/connect-service-upstreams': 'web:1234,web-admin:2234' 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 ``` If you exec on to a static-client pod, using a command like: ```shell-session $ kubectl exec -it static-client-5bd667fbd6-kk6xs -- /bin/sh ``` you can then run: ```shell-session $ curl localhost:1234 ``` to see the output `hello world` and run: ```shell-session $ curl localhost:2234 ``` to see the output `hello world from 9090`. The way this works is that a Consul service instance is being registered per port on the Pod, so there are 2 Consul services in this case. An additional Envoy sidecar proxy and `connect-init` init container are also deployed per port in the Pod. So the upstream configuration can use the individual service names to reach each port as seen in the example. #### Caveats for Multi-port Pods * Transparent proxy is not supported for multi-port Pods. * Metrics and metrics merging is not supported for multi-port Pods. * Upstreams will only be set on the first service's Envoy sidecar proxy for the pod. * This means that ServiceIntentions from a multi-port pod to elsewhere, will need to use the first service's name, `web` in the example above to accept connections from either `web` or `web-admin`. ServiceIntentions from elsewhere to a multi-port pod can use the individual service names within the multi-port Pod. * Health checking is done on a per-Pod basis, so if any Kubernetes health checks (like readiness, liveness, etc) are failing for any container on the Pod, the entire Pod is marked unhealthy, and any Consul service referencing that Pod will also be marked as unhealthy. So, if `web` has a failing health check, `web-admin` would also be marked as unhealthy for service mesh traffic. ## Installation and Configuration The service mesh sidecar proxy is injected via a [mutating admission webhook](https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks) call the connect injector 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](/consul/docs/k8s/installation/install). To install the connect injector, enable the connect injection feature using [Helm values](/consul/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 ``` 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. ### Verifying the Installation To verify the installation, run the ["Accepting Inbound Connections"](/consul/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 connect injected 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. ### 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](/consul/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](/consul/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/docs/k8s/annotations-and-labels#consul-hashicorp-com-connect-service-upstreams) for more details. -> **Note:** When you specify upstreams via an upstreams annotation, you will need to use `localhost:` with the port from the upstreams annotation instead of KubeDNS to connect to your upstream application.