mirror of https://github.com/hashicorp/consul
325 lines
13 KiB
Markdown
325 lines
13 KiB
Markdown
---
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layout: "docs"
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page_title: "Running Consul - Kubernetes"
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sidebar_current: "docs-platform-k8s-run"
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description: |-
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Consul can run directly on Kubernetes, both in server or client mode. For pure-Kubernetes workloads, this enables Consul to also exist purely within Kubernetes. For heterogeneous workloads, Consul agents can join a server running inside or outside of Kubernetes.
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---
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# Running Consul on Kubernetes
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Consul can run directly on Kubernetes, both in server or client mode.
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For pure-Kubernetes workloads, this enables Consul to also exist purely
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within Kubernetes. For heterogeneous workloads, Consul agents can join
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a server running inside or outside of Kubernetes.
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This page starts with a large how-to section for various specific tasks.
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To learn more about the general architecture of Consul on Kubernetes, scroll
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down to the [architecture](/docs/platform/k8s/run.html#architecture) section.
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## Helm Chart
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The recommended way to run Consul on Kubernetes is via the
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[Helm chart](/docs/platform/k8s/helm.html). This will install and configure
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all the necessary components to run Consul. The configuration enables you
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to run just a server cluster, just a client cluster, or both. Using the Helm
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chart, you can have a full Consul deployment up and running in seconds.
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While the Helm chart exposes dozens of useful configurations and automatically
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sets up complex resources, it **does not automatically operate Consul.**
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You are still responsible for learning how to monitor, backup,
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upgrade, etc. the Consul cluster.
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The Helm chart has no required configuration and will install a Consul
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cluster with sane defaults out of the box. Prior to going to production,
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it is highly recommended that you
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[learn about the configuration options](/docs/platform/k8s/helm.html#configuration-values-).
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~> **Security Warning:** By default, the chart will install an insecure configuration
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of Consul. This provides a less complicated out-of-box experience for new users,
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but is not appropriate for a production setup. It is highly recommended to use
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a properly secured Kubernetes cluster or make sure that you understand and enable
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the [recommended security features](/docs/internals/security.html). Currently,
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some of these features are not supported in the Helm chart and require additional
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manual configuration.
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## How-To
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### Installing Consul
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To install Consul, clone the consul-helm repository, checkout the latest release, and install
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Consul. You can run `helm install` with the `--dry-run` flag to see the
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resources it would configure. In a production environment, you should always
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use the `--dry-run` flag prior to making any changes to the Consul cluster
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via Helm.
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```sh
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# Clone the chart repo
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$ git clone https://github.com/hashicorp/consul-helm.git
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$ cd consul-helm
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# Checkout a tagged version
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$ git checkout v0.1.0
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# Run Helm
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$ helm install --name consul ./
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...
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```
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_That's it._ The Helm chart does everything to setup a recommended
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Consul-on-Kubernetes deployment.
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In a couple minutes, a Consul cluster will be formed and a leader
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elected and every node will have a running Consul agent.
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The defaults will install both server and client agents. To install
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only one or the other, see the
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[chart configuration values](/docs/platform/k8s/helm.html#configuration-values-).
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### Viewing the Consul UI
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The Consul UI is enabled by default when using the Helm chart.
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For security reasons, it isn't exposed via a Service by default so you must
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use `kubectl port-forward` to visit the UI. Once the port is forwarded as
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shown below, navigate your browser to `http://localhost:8500`.
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```
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$ kubectl port-forward consul-server-0 8500:8500
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...
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```
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The UI can also be exposed via a Kubernetes Service. To do this, configure
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the [`ui.service` chart values](/docs/platform/k8s/helm.html#v-ui-service).
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### Joining an Existing Consul Cluster
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If you have a Consul cluster already running, you can configure your
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Kubernetes nodes to join this existing cluster.
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```yaml
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global:
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enabled: false
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client:
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enabled: true
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join:
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- "provider=my-cloud config=val ..."
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```
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The `values.yaml` file to configure the Helm chart sets the proper
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configuration to join an existing cluster.
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The `global.enabled` value first disables all chart components by default
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so that each component is opt-in. This allows us to _only_ setup the client
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agents. We then opt-in to the client agents by setting `client.enabled` to
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`true`.
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Next, `client.join` is set to an array of valid
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[`-retry-join` values](/docs/agent/options.html#retry-join). In the
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example above, a fake [cloud auto-join](/docs/agent/cloud-auto-join.html)
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value is specified. This should be set to resolve to the proper addresses of
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your existing Consul cluster.
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-> **Networking:** Note that for the Kubernetes nodes to join an existing
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cluster, the nodes (and specifically the agent pods) must be able to connect
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to all other server and client agents inside and _outside_ of Kubernetes.
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If this isn't possible, consider running the Kubernetes agents as a separate
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DC or adopting Enterprise for
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[network segments](/docs/enterprise/network-segments/index.html).
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### Accessing the Consul HTTP API
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The Consul HTTP API should be accessed by communicating to the local agent
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running on the same node. While technically any listening agent (client or
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server) can respond to the HTTP API, communicating with the local agent
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has important caching behavior, and allows you to use the simpler
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[`/agent` endpoints for services and checks](/api/agent.html).
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For Consul installed via the Helm chart, a client agent is installed on
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each Kubernetes node. This is explained in the [architecture](/docs/platform/k8s/run.html#client-agents)
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section. To access the agent, you may use the
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[downward API](https://kubernetes.io/docs/tasks/inject-data-application/downward-api-volume-expose-pod-information/).
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An example pod specification is shown below. In addition to pods, anything
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with a pod template can also access the downward API and can therefore also
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access Consul: StatefulSets, Deployments, Jobs, etc.
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```yaml
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apiVersion: v1
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kind: Pod
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metadata:
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name: consul-example
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spec:
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containers:
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- name: example
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image: "consul:latest"
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env:
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- name: HOST_IP
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valueFrom:
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fieldRef:
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fieldPath: status.hostIP
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command:
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- "/bin/sh"
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- "-ec"
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- |
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export CONSUL_HTTP_ADDR="${HOST_IP}:8500"
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consul kv put hello world
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restartPolicy: Never
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```
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An example `Deployment` is also shown below to show how the host IP can
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be accessed from nested pod specifications:
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```yaml
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apiVersion: apps/v1
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kind: Deployment
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metadata:
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name: consul-example-deployment
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spec:
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replicas: 1
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selector:
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matchLabels:
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app: consul-example
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template:
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metadata:
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labels:
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app: consul-example
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spec:
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containers:
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- name: example
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image: "consul:latest"
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env:
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- name: HOST_IP
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valueFrom:
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fieldRef:
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fieldPath: status.hostIP
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command:
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- "/bin/sh"
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- "-ec"
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- |
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export CONSUL_HTTP_ADDR="${HOST_IP}:8500"
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consul kv put hello world
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```
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### Upgrading Consul on Kubernetes
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To upgrade Consul on Kubernetes, we follow the same pattern as
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[generally upgrading Consul](/docs/upgrading.html), except we can use
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the Helm chart to step through a rolling deploy. It is important to understand
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how to [generally upgrade Consul](/docs/upgrading.html) before reading this
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section.
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Upgrading Consul on Kubernetes will follow the same pattern: each server
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will be updated one-by-one. After that is successful, the clients will
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be updated in batches.
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#### Upgrading Consul Servers
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To initiate the upgrade, change the `server.image` value to the
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desired Consul version. For illustrative purposes, the example below will
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use `consul:123.456`. Also set the `server.updatePartition` value
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_equal to the number of server replicas_:
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```yaml
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server:
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image: "consul:123.456"
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replicas: 3
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updatePartition: 3
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```
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The `updatePartition` value controls how many instances of the server
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cluster are updated. Only instances with an index _greater than_ the
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`updatePartition` value are updated (zero-indexed). Therefore, by setting
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it equal to replicas, none should update yet.
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Next, run the upgrade. You should run this with `--dry-run` first to verify
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the changes that will be sent to the Kubernetes cluster.
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```
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$ helm upgrade consul ./
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...
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```
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This should cause no changes (although the resource will be updated). If
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everything is stable, begin by decreasing the `updatePartition` value by one,
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and running `helm upgrade` again. This should cause the first Consul server
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to be stopped and restarted with the new image.
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Wait until the Consul server cluster is healthy again (30s to a few minutes)
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then decrease `updatePartition` and upgrade again. Continue until
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`updatePartition` is `0`. At this point, you may remove the
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`updatePartition` configuration. Your server upgrade is complete.
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#### Upgrading Consul Clients
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With the servers upgraded, it is time to upgrade the clients. To upgrade
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the clients, set the `client.image` value to the desired Consul version.
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Then, run `helm upgrade`. This will upgrade the clients in batches, waiting
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until the clients come up healthy before continuing.
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## Architecture
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We recommend running Consul on Kubernetes with the same
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[general architecture](/docs/internals/architecture.html)
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as running it anywhere else. There are some benefits Kubernetes can provide
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that eases operating a Consul cluster and we document those below. The standard
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[production deployment guide](https://learn.hashicorp.com/consul/datacenter-deploy/deployment-guide) is still an
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important read even if running Consul within Kubernetes.
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Each section below will outline the different components of running Consul
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on Kubernetes and an overview of the resources that are used within the
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Kubernetes cluster.
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### Server Agents
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The server agents are run as a **StatefulSet**, using persistent volume
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claims to store the server state. This also ensures that the
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[node ID](/docs/agent/options.html#_node_id) is persisted so that servers
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can be rescheduled onto new IP addresses without causing issues. The server agents
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are configured with
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[anti-affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#affinity-and-anti-affinity)
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rules so that they are placed on different nodes. A readiness probe is
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configured that marks the pod as ready only when it has established a leader.
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A **Service** is registered to represent the servers and expose the various
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ports. The DNS address of this service is used to join the servers to each
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other without requiring any other access to the Kubernetes cluster. The
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service is configured to publish non-ready endpoints so that it can be used
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for joining during bootstrap and upgrades.
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Additionally, a **PodDisruptionBudget** is configured so the Consul server
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cluster maintains quorum during voluntary operational events. The maximum
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unavailable is `(n/2)-1` where `n` is the number of server agents.
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-> **Note:** Kubernetes and Helm do not delete Persistent Volumes or Persistent
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Volume Claims when a
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[StatefulSet is deleted](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#stable-storage),
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so this must done manually when removing servers.
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### Client Agents
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The client agents are run as a **DaemonSet**. This places one agent
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(within its own pod) on each Kubernetes node.
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The clients expose the Consul HTTP API via a static port (default 8500)
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bound to the host port. This enables all other pods on the node to connect
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to the node-local agent using the host IP that can be retrieved via the
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Kubernetes downward API. See
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[accessing the Consul HTTP API](/docs/platform/k8s/run.html#accessing-the-consul-http-api)
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for an example.
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There is a major limitation to this: there is no way to bind to a local-only
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host port. Therefore, any other node can connect to the agent. This should be
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considered for security. For a properly production-secured agent with TLS
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and ACLs, this is safe.
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Some people prefer to run **Consul agent per pod** architectures, since this
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makes it easy to register the pod as a service. However, this turns
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a pod into a "node" in Consul and also causes an explosion of resource usage
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since every pod needs a Consul agent. We recommend instead running an
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agent (in a dedicated pod) per node, via the DaemonSet. This maintains the
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node equivalence in Consul. Service registration should be handled via the
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catalog syncing feature with Services rather than pods.
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-> **Note:** Due to a limitation of anti-affinity rules with DaemonSets,
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a client-mode agent runs alongside server-mode agents in Kubernetes. This
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duplication wastes some resources, but otherwise functions perfectly fine.
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