193 lines
8.9 KiB
Markdown
193 lines
8.9 KiB
Markdown
---
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layout: "docs"
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page_title: "Kubernetes Consul Reference Architecture"
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sidebar_current: "docs-guides-k8s-reference-architecture"
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description: |-
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This document provides recommended practices and a reference architecture.
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---
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# Consul and Kubernetes Reference Architecture
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Preparing your Kubernetes cluster to successfully deploy and run Consul is an
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important first step in your production deployment process. In this guide you
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will prepare your Kubernetes cluster, that can be running on any platform
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(AKS, EKS, GKE, etc). However, we will call out cloud specific differences when
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applicable. Before starting this guide you should have experience with
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Kubernetes, and have `kubectl` and helm configured locally.
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By the end of this guide, you will be able to select the right resource limits
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for Consul pods, select the Consul datacenter design that meets your use case,
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and understand the minimum networking requirements.
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## Infrastructure Requirements
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Consul server agents are responsible for the cluster state, responding to RPC
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queries, and processing all write operations. Since the Consul servers are
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highly active and are responsible for maintaining the cluster state, server
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sizing is critical for the overall performance, efficiency, and health of the
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Consul cluster. Review the [Consul Reference
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Architecture](/consul/advanced/day-1-operations/reference-architecture#consul-servers)
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guide for sizing recommendations for small and large Consul datacenters.
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The CPU and memory recommendations can be used when you select the resources
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limits for the Consul pods. The disk recommendations can also be used when
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selecting the resources limits and configuring persistent volumes. You will
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need to set both `limits` and `requests` in the Helm chart. Below is an example
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snippet of Helm config for a Consul server in a large environment.
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```yaml
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# values.yaml
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server
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resources: |
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requests:
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memory: "32Gi"
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cpu: "4"
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limits:
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memory: "32Gi"
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cpu: "4"
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storage: 50Gi
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...
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```
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You should also set [resource limits for Consul
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clients](https://www.consul.io/docs/platform/k8s/helm.html#v-client-resources),
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so that the client pods do not unexpectedly consume more resources than
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expected.
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[Persistent
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volumes](https://kubernetes.io/docs/concepts/storage/persistent-volumes/) (PV)
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allow you to have a fixed disk location for the Consul data. This ensures that
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if a Consul server is lost, the data will not be lost. This is an important
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feature of Kubernetes, but may take some additional configuration. If you are
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running Kubernetes on one of the major cloud platforms, persistent volumes
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should already be configured for you; be sure to read their documentation for more
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details. If you are setting up the persistent volumes resource in Kubernetes, you may need
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to map the Consul server to that volume with the [storage class
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parameter](https://www.consul.io/docs/platform/k8s/helm.html#v-server-storageclass).
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Finally, you will need to enable RBAC on your Kubernetes cluster. Review
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the [Kubernetes
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RBAC](https://kubernetes.io/docs/reference/access-authn-authz/rbac/) documenation. You
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should also review RBAC and authentication documentation if your Kubernetes cluster
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is running on a major cloud platorom.
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- [AWS](https://docs.aws.amazon.com/eks/latest/userguide/managing-auth.html).
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- [GCP](https://cloud.google.com/kubernetes-engine/docs/how-to/role-based-access-control).
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- [Azure](https://docs.microsoft.com/en-us/cli/azure/aks?view=azure-cli-latest#az-aks-create). In Azure, RBAC is enabled by default.
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## Datacenter Design
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There are many possible configurations for running Consul with Kubernetes. In this guide
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we will cover three of the most common.
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1. Consul agents can be solely deployed within Kubernetes.
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1. Consul servers
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can be deployed outside of Kubernetes and clients inside of Kubernetes.
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1. Multiple Consul datacenters with agents inside and outside of Kubernetes.
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Review the Consul Kubernetes-specific
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[documentation](https://www.consul.io/docs/platform/k8s/index.html#use-cases)
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for additional use case information.
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Since all three use cases will also need catalog sync, review the
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implementation [details for catalog sync](https://www.consul.io/docs/platform/k8s/service-sync.html).
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### Consul Datacenter Deployed in Kubernetes
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Deploying a Consul cluster, servers and clients, in Kubernetes can be done with
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the official [Helm
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chart](https://www.consul.io/docs/platform/k8s/helm.html#using-the-helm-chart).
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This configuration is useful for managing services within Kubernetes and is
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common for users who do not already have a production Consul datacenter.
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The Consul datacenter in Kubernetes will function the same as a platform
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independent Consul datacenter, such as Consul clusters deployed on bare metal servers
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or virtual machines. Agents will communicate over LAN gossip, servers
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will participate in the Raft consensus, and client requests will be
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forwarded to the servers via RPCs.
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### Consul Datacenter with a Kubernetes Cluster
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To use an existing Consul cluster to manage services in Kubernetes, Consul
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clients can be deployed within the Kubernetes cluster. This will also allow
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Kubernetes-defined services to be synced to Consul. This design allows Consul tools
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such as envconsul, consul-template, and more to work on Kubernetes.
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This type of deployment in Kubernetes can also be set up with the official Helm
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chart.
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### Multiple Consul Clusters with a Kubernetes Cluster
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Consul clusters in different datacenters running the same service can be joined
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by WAN links. The clusters can operate independently and only communicate over
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the WAN. This type datacenter design is detailed in the [Reference Architecture
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guide](/consul/advanced/day-1-operations/reference-architecture#multiple-datacenters).
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In this setup, you can have a Consul cluster running outside of Kubernetes and
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a Consul cluster running inside of Kubernetes.
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### Catalog Sync
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To use catalog sync, you must enable it in the [Helm
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chart](https://www.consul.io/docs/platform/k8s/helm.html#v-synccatalog).
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Catalog sync allows you to sync services between Consul and Kubernetes. The
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sync can be unidirectional in either direction or bidirectional. Read the
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[documentation](https://www.consul.io/docs/platform/k8s/service-sync.html) to
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learn more about the configuration.
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Services synced from Kubernetes to Consul will be discoverable, like any other
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service within the Consul datacenter. Read more in the [network
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connectivity](#networking-connectivity) section to learn more about related
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Kubernetes configuration. Services synced from Consul to Kubernetes will be
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discoverable with the built-in Kubernetes DNS once a [Consul stub
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domain](https://www.consul.io/docs/platform/k8s/dns.html) is deployed. When
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bidirectional catalog sync is enabled, it will behave like the two
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unidirectional setups.
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## Networking Connectivity
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When running Consul as a pod inside of Kubernetes, the Consul servers will be
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automatically configured with the appropriate addresses. However, when running
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Consul servers outside of the Kubernetes cluster and clients inside Kubernetes
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as pods, there are additional [networking
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considerations](/consul/advanced/day-1-operations/reference-architecture#network-connectivity).
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### Network Connectivity for Services
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When using Consul catalog sync, to sync Kubernetes services to Consul, you will
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need to ensure the Kubernetes services are supported [service
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types](https://www.consul.io/docs/platform/k8s/service-sync.html#kubernetes-service-types)
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and configure correctly in Kubernetes. If the service is configured correctly,
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it will be discoverable by Consul like any other service in the datacenter.
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~> Warning: You are responsible for ensuring that external services can communicate
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with services deployed in the Kubernetes cluster. For example, `ClusterIP` type services
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may not be directly accessible by IP address from outside the Kubernetes cluster
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for some Kubernetes configurations.
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### Network Security
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Finally, you should consider securing your Consul datacenter with
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[ACLs](/consul/advanced/day-1-operations/production-acls). ACLs should be used with [Consul
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Connect](https://www.consul.io/docs/platform/k8s/connect.html) to secure
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service to service communication. The Kubernetes cluster should also be
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secured.
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## Summary
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You are now prepared to deploy Consul with Kubernetes. In this
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guide, you were introduced to several a datacenter design for a variety of use
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cases. This guide also outlined the Kubernetes prerequisites, resource
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requirements for Consul, and networking considerations. Continue onto the
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[Deploying Consul with Kubernetes
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guide](/consul/getting-started-k8s/helm-deploy) for
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information on deploying Consul with the official Helm chart or continue
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reading about Consul Operations in the [Day 1 Path](https://learn.hashicorp.com/consul/?track=advanced#advanced).
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