297 lines
12 KiB
Markdown
297 lines
12 KiB
Markdown
---
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layout: "docs"
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page_title: "Service Sync - Kubernetes"
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sidebar_current: "docs-platform-k8s-service-sync"
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description: |-
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The services in Kubernetes and Consul can be automatically synced so that Kubernetes services are available to Consul agents and services in Consul can be available as first-class Kubernetes services.
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---
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# Syncing Kubernetes and Consul Services
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The services in Kubernetes and Consul can be automatically synced so that Kubernetes
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services are available to Consul agents and services in Consul can be available
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as first-class Kubernetes services. This functionality is provided by the
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[consul-k8s project](https://github.com/hashicorp/consul-k8s) and can be
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automatically installed and configured using the
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[Consul Helm chart](/docs/platform/k8s/helm.html).
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**Why sync Kubernetes services to Consul?** Kubernetes services synced to the
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Consul catalog enable Kubernetes services to be accessed by any node that
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is part of the Consul cluster, including other distinct Kubernetes clusters.
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For non-Kubernetes nodes, they can access services using the standard
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[Consul DNS](/docs/agent/dns.html) or HTTP API.
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**Why sync Consul services to Kubernetes?** Syncing Consul services to
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Kubernetes services enables non-Kubernetes services (such as external to
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the cluster) to be accessed in a native Kubernetes way: using kube-dns,
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environment variables, etc. This makes it very easy to automate external
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service discovery, including hosted services like databases.
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## Installation and Configuration
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The service sync is done using an external long-running process in the
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[consul-k8s project](https://github.com/hashicorp/consul-k8s). This process
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can run either in or out of a Kubernetes cluster. However, running this within
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the Kubernetes cluster is generally easier since it is automated using the
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[Helm chart](/docs/platform/k8s/helm.html).
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The Consul server cluster can run either in or out of a Kubernetes cluster.
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The Consul server cluster does not need to be running on the same machine
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or same platform as the sync process. The sync process needs to be configured
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with the address to the Consul cluster as well as any additional access
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information such as ACL tokens.
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To install the sync, enable the catalog sync feature using
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[Helm values](/docs/platform/k8s/helm.html#configuration-values-) and
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upgrade the installation using `helm upgrade` for existing installs or
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`helm install` for a fresh install.
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```yaml
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syncCatalog:
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enabled: true
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```
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This will enable services to sync _in both directions_. You can also choose
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to only sync Kubernetes services to Consul or vice versa by disabling a direction.
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See the [Helm configuration](/docs/platform/k8s/helm.html#configuration-values-)
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for more information.
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-> **Before installing,** please read the introduction paragraphs for the
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reference documentation below for both
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[Kubernetes to Consul](/docs/platform/k8s/service-sync.html#kubernetes-to-consul) and
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[Consul to Kubernetes](/docs/platform/k8s/service-sync.html#consul-to-kubernetes)
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sync to understand how the syncing works.
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### Authentication
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The sync process must authenticate to both Kubernetes and Consul to read
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and write services.
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For Kubernetes, a valid kubeconfig file must be provided with cluster
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and authentication information. The sync process will look into the default locations
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for both in-cluster and out-of-cluster authentication. If `kubectl` works,
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then the sync program should work.
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For Consul, if ACLs are configured on the cluster, a Consul
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[ACL token](https://learn.hashicorp.com/consul/advanced/day-1-operations/acl-guide)
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will need to be provided. Review the [ACL rules](/docs/agent/acl-rules.html)
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when creating this token so that it only allows the necessary privileges. The catalog
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sync process accepts this token by using the [`CONSUL_HTTP_TOKEN`](/docs/commands/index.html#consul_http_token)
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environment variable. This token should be set as a
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[Kubernetes secret](https://kubernetes.io/docs/concepts/configuration/secret/#creating-your-own-secrets)
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and referenced in the Helm chart.
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## Kubernetes to Consul
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This sync registers Kubernetes services to the Consul catalog automatically.
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This enables discovery and connection to Kubernetes services using native
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Consul service discovery such as DNS or HTTP. This is particularly useful for
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non-Kubernetes nodes. This also causes all discoverable services to be part of
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a central service catalog in Consul for further syncing into alternate
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Kubernetes clusters or other platforms.
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### Kubernetes Service Types
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Not all Kubernetes services are externally accessible. The sync program by
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default will only sync services of the following types or configurations.
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If a service type is not listed below, then the sync program will ignore that
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service type.
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#### NodePort
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[NodePort services](https://kubernetes.io/docs/concepts/services-networking/service/#nodeport)
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register a static port that every node in the K8S cluster listens on.
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For NodePort services, a Consul service instance will be created for each
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node that has the representative pod running. While Kubernetes configures
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a static port on all nodes in the cluster, this limits the number of service
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instances to be equal to the nodes running the target pods.
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The service instances will be registered to the Kubernetes node name
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that each instance lives on. This is guaranteed unique by Kubernetes. An
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existing node entry will be used if it is already part of the Consul
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cluster (for example if you're running a client agent on all Kubernetes
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nodes). This allows the normal agent health checks for that node to continue
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working.
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#### LoadBalancer
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For LoadBalancer services, a single service instance will be registered with
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the external IP of the created load balancer. Because this is already a load
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balancer, only one service instance will be registered with Consul rather
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than registering each individual pod endpoint.
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#### External IPs
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Any service type may specify an
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"[external IP](https://kubernetes.io/docs/concepts/services-networking/service/#external-ips)"
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configuration. The external IP must be configured by some other system, but
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any service discovery will resolve to this set of IP addresses rather than a
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virtual IP.
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If an external IP list is present, a service instance in Consul will be created
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for each external IP. It is assumed that if an external IP is present that it
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is routable and configured by some other system.
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#### ClusterIP
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ClusterIP services are synced by default as of `consul-k8s` version 0.3.0. In
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many Kubernetes clusters, ClusterIPs may not be accessible outside of the cluster,
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so you may end up with services registered in Consul that are not routable. To
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skip syncing ClusterIP services, set [`syncClusterIPServices`](/docs/platform/k8s/helm.html#v-synccatalog-clusterip-sync)
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to `false` in the Helm chart values file.
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### Sync Enable/Disable
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By default, all valid services (as explained above) are synced. This default can
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be changed using the [configuration](/docs/platform/k8s/helm.html#v-synccatalog-default).
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Syncing can also be explicitly enabled or disabled using an
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annotation:
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```yaml
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kind: Service
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apiVersion: v1
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metadata:
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name: my-service
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annotations:
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"consul.hashicorp.com/service-sync": "false"
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```
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### Service Name
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When a Kubernetes service is synced to Consul, the name of the service in Consul
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by default will be the value of the "name" metadata on that Kubernetes service.
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This makes it so that service sync works with zero configuration changes.
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This can be overridden using an annotation to specify the Consul service name:
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```yaml
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kind: Service
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apiVersion: v1
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metadata:
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name: my-service
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annotations:
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"consul.hashicorp.com/service-name": my-consul-service
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```
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**If a conflicting service name exists in Consul,** the sync program will
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register additional instances to that same service. Therefore, services inside
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and outside of Kubernetes should have different names unless you want either
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side to potentially connect. This default behavior also enables gracefully
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transitioning a service from outside of K8S to inside, and vice versa.
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### Service Ports
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When syncing the Kubernetes service to Consul, the Consul service port will be
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the first defined port in the service. Additionally, all ports will be
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registered in the service instance metadata with the key "port-X" where X is
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the name of the port and the value is the externally accessible port.
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The default service port can be overridden using an annotation:
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```yaml
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kind: Service
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apiVersion: v1
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metadata:
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name: my-service
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annotations:
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"consul.hashicorp.com/service-port": "http"
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```
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The annotation value may be a name of a port (recommended) or an exact port value.
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### Service Tags
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A service registered in Consul from Kubernetes will always have the tag "k8s" added
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to it. Additional tags can be specified with a comma-separated annotation value
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as shown below. This will also automatically include the "k8s" tag which can't
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be disabled. The values should be specified comma-separated without any
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additional whitespace.
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```yaml
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kind: Service
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apiVersion: v1
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metadata:
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name: my-service
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annotations:
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"consul.hashicorp.com/service-tags": "primary,foo"
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```
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### Service Meta
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A service registered in Consul from Kubernetes will set the `external-source` key to
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"kubernetes". This can be used by API consumers, the UI, CLI, etc. to filter
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service instances that are set in k8s. The Consul UI (in Consul 1.2.3 and later)
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will read this value to show a Kubernetes icon next to all externally
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registered services from Kubernetes.
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Additional metadata can be specified using annotations. The "KEY" below can be
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set to any key. This allows setting multiple meta values:
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```yaml
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kind: Service
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apiVersion: v1
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metadata:
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name: my-service
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annotations:
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"consul.hashicorp.com/service-meta-KEY": "value"
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```
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## Consul to Kubernetes
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This syncs Consul services into first-class Kubernetes services.
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Each Consul service is synced to an
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[ExternalName](https://kubernetes.io/docs/concepts/services-networking/service/#externalname)
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service in Kubernetes. The external name is configured to be the Consul
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DNS entry.
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This enables external services to be discovered using native Kubernetes
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tooling. This can be used to ease software migration into or out of Kubernetes,
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across platforms, to and from hosted services, and more.
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-> **Requires Consul DNS via CoreDNS in Kubernetes:** This feature requires that
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[Consul DNS](/docs/platform/k8s/dns.html) is configured within Kubernetes.
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Additionally, **[CoreDNS](https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/#config-coredns)
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is required (instead of kube-dns)** to resolve an
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issue with resolving `externalName` services pointing to custom domains.
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In the future we hope to remove this requirement by syncing the instance
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addresses directly into service endpoints.
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### Sync Enable/Disable
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All Consul services visible to the sync process based on its given ACL token
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will be synced to Kubernetes.
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There is no way to change this behavior per service. For the opposite sync
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direction (Kubernetes to Consul), you can use Kubernetes annotations to disable
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a sync per service. This is not currently possible for Consul to Kubernetes
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sync and the ACL token must be used to limit what services are synced.
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In the future, we hope to support per-service configuration.
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### Service Name
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When a Consul service is synced to Kubernetes, the name of the Kubernetes
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service will exactly match the name of the Consul service.
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To change this default exact match behavior, it is possible to specify a
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prefix to be added to service names within Kubernetes by using the
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`-k8s-service-prefix` flag. This can also be specified in the Helm
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configuration.
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**If a conflicting service is found,** the service will not be synced. This
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does not match the Kubernetes to Consul behavior, but given the current
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implementation we must do this because Kubernetes can't mix both CNAME and
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Endpoint-based services.
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### Kubernetes Service Labels and Annotations
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Any Consul services synced to Kubernetes will be labeled and annotated.
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An annotation `consul.hashicorp.com/synced` will be set to "true" to note
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that this is a synced service from Consul.
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Additionally, a label `consul=true` will be specified so that label selectors
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can be used with `kubectl` and other tooling to easily filter all Consul-synced
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services.
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