441 lines
17 KiB
Plaintext
441 lines
17 KiB
Plaintext
---
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layout: docs
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page_title: Service Sync for Consul on Kubernetes
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description: >-
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Service sync is a Consul on Kubernetes feature that makes Kubernetes and Consul services available to each other. Learn how to configure Helm values so services can communicate and make Kubernetes services appear in the Consul UI.
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---
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# Service Sync for Consul on Kubernetes
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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](/consul/docs/k8s/installation/install).
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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](/consul/docs/discovery/dns) 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 to be accessed using kube-dns and Kubernetes-specific
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environment variables. This integration 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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~> Enabling both Service Mesh and Service Sync on the same Kubernetes services is not supported, as Service Mesh also registers Kubernetes service instances to Consul. Ensure that Service Sync is only enabled for namespaces and services that are not injected with the Consul sidecar for Service Mesh as described in [Sync Enable/Disable](/consul/docs/k8s/service-sync#sync-enable-disable).
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The service sync uses 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 inside or outside of a Kubernetes cluster. However, running this process within
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the Kubernetes cluster is generally easier since it is automated using the
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[Helm chart](/consul/docs/k8s/helm).
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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 a Consul agent as well as any additional access
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information such as ACL tokens.
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To install the sync process, enable the catalog sync feature using
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[Helm values](/consul/docs/k8s/helm#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 value enables service syncing in both direction. You can also disable a direction so that only Kubernetes services sync to Consul, or only Consul services sync to Kubernetes.
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To only enable syncing Consul services to Kubernetes use the config:
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```yaml
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syncCatalog:
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enabled: true
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toConsul: false
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toK8S: true
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```
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To only enable syncing Kubernetes services to Consul use:
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```yaml
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syncCatalog:
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enabled: true
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toConsul: true
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toK8S: false
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```
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Refer to the [Helm configuration](/consul/docs/k8s/helm#v-synccatalog)
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for more information.
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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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If running `consul-k8s` using the Helm chart, then this authentication is handled for you.
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If running `consul-k8s` outside of Kubernetes, a valid kubeconfig file must be provided with cluster
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and authentication information. The sync process looks 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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If ACLs are configured on the Consul cluster, you need to provide a Consul
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[ACL token](/consul/tutorials/security/access-control-setup-production). Review the [ACL rules](/consul/docs/security/acl/acl-rules)
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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`](/consul/commands#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 sync enables discovery and connection to Kubernetes services using native
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Consul service discovery protocols 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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Each synced service is registered onto a Consul node called `k8s-sync`. This node
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is not a real node. Instead, the catalog sync process is monitoring Kubernetes
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and syncing the services to Consul.
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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 only syncs services of the following types or configurations.
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If a service type is not listed below, then the sync program ignores 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 is 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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By default it uses the external IP of the node but this can be configured through
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the [`nodePortSyncType` helm option](/consul/docs/k8s/helm#v-synccatalog-nodeportsynctype).
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The service instance's port is set to the first defined node port of the service unless
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set specifically in the `consul.hashicorp.com/service-port` annotation. Refer to [Service Ports](/consul/docs/k8s/service-sync#service-ports) for more information.
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#### LoadBalancer
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For LoadBalancer services, a single service instance is 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 is registered with Consul rather
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than registering each individual pod endpoint.
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The service instance's port is set to the first defined port of the
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service unless set specifically in the `consul.hashicorp.com/service-port` annotation. Refer to [Service Ports](/consul/docs/k8s/service-sync#service-ports) for more information.
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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 resolves 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 is 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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The service instance's port is set to the _first_ defined port of the
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service unless set specifically with the `consul.hashicorp.com/service-port` annotation. Refer to [Service Ports](/consul/docs/k8s/service-sync#service-ports) for more information.
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#### ClusterIP
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ClusterIP services are synced by default as of `consul-k8s` version 0.3.0.
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Each pod that is an endpoint for the service is synced as a Consul service
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instance with its IP set to the pod IP and its port set to the `targetPort`.
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The service instance's port can be overridden with the `consul.hashicorp.com/service-port` annotation. Refer to [Service Ports](/consul/docs/k8s/service-sync#service-ports) for more information.
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-> In Kubernetes clusters where pod IPs are not accessible outside the cluster,
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the services registered in Consul may not be routable. To
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skip syncing ClusterIP services, set [`syncClusterIPServices`](/consul/docs/k8s/helm#v-synccatalog-syncclusteripservices)
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to `false` in the Helm chart values file.
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### Enable and disable sync
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By default, all valid service types are synced from every Kubernetes
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namespace except for `kube-system` and `kube-public`.
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To only sync specific services, first modify the annotation to set the default to `false`:
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```yaml
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syncCatalog:
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enabled: true
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default: false
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```
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Then, explicitly enable syncing specific services with the `consul.hashicorp.com/service-sync` 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': 'true'
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```
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-> **Note:** If the annotation is set to `false` when the default sync is `true`, the service does not sync.
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You can allow or deny syncing from specific Kubernetes namespaces by setting the
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`k8sAllowNamespaces` and `k8sDenyNamespaces` keys:
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```yaml
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syncCatalog:
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enabled: true
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default: true
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k8sAllowNamespaces: ['*']
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k8sDenyNamespaces: ['kube-system', 'kube-public']
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```
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In the default configuration, services from all namespaces except for
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`kube-system` and `kube-public` are synced.
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To only sync from specific namespaces, you can list only those
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namespaces in the `k8sAllowNamespaces` key:
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```yaml
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syncCatalog:
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enabled: true
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default: true
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k8sAllowNamespaces: ['my-ns-1', 'my-ns-2']
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k8sDenyNamespaces: []
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```
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To sync from every namespace except specific namespaces, use `*` in the allow list and then specify the non-syncing namespaces in the deny list:
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```yaml
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syncCatalog:
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enabled: true
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default: true
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k8sAllowNamespaces: ['*']
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k8sDenyNamespaces: ['no-sync-ns-1', 'no-sync-ns-2']
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```
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-> **Note:** The deny list takes precedence over the allow list. If a namespace
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is listed in both lists, it does not sync.
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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 is 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 setting 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
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registers 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 between deployments inside and outside of Kubernetes.
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### Service ports
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When syncing the Kubernetes service to Consul, the Consul service port is the first defined port in the service. Additionally, all ports become 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 always has the tag "k8s" added
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to it. Additional tags can be specified with a comma-separated annotation value. These custom tags automatically include the "k8s" tag, which can't be disabled. When specifying values, use commas without 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 sets the `external-source` key to
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`kubernetes`. This can be used from the APLI, CLI and UI to filter
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service instances that are set in k8s. The Consul UI displays 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 Enterprise Namespaces
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Consul Enterprise supports Consul namespaces. These can be used when syncing
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from Kubernetes to Consul. However, namespaces are not supported when syncing from Consul to Kubernetes.
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There are three options available:
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1. **Single Destination Namespace** – Sync all Kubernetes services, regardless of namespace,
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into the same Consul namespace.
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```yaml
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global:
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enableConsulNamespaces: true
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syncCatalog:
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enabled: true
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consulNamespaces:
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consulDestinationNamespace: 'my-consul-ns'
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```
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1. **Mirror Namespaces** - Each Kubernetes service is synced to a Consul namespace with the same
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name as its Kubernetes namespace.
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For example, service `foo` in Kubernetes namespace `ns-1` is synced to the Consul namespace `ns-1`.
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If a mirrored namespace does not exist in Consul, it is created automatically.
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```yaml
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global:
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enableConsulNamespaces: true
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syncCatalog:
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enabled: true
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consulNamespaces:
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mirroringK8S: true
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addK8SNamespaceSuffix: false
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```
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1. **Mirror Namespaces With Prefix** - Each Kubernetes service is synced to a Consul namespace
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with the same name as its Kubernetes namespace with a prefix. For example, given a prefix
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`k8s-`, service `foo` in Kubernetes namespace `ns-1` syncs to the Consul namespace
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`k8s-ns-1`.
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```yaml
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global:
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enableConsulNamespaces: true
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syncCatalog:
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enabled: true
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consulNamespaces:
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mirroringK8S: true
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mirroringK8SPrefix: 'k8s-'
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addK8SNamespaceSuffix: false
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```
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-> Note that in both mirroring examples, `addK8SNamespaceSuffix` is set to `false`. If set to its default value, `true`, the Kubernetes namespace is added as a suffix to each
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Consul service name. For example Kubernetes service `foo` in namespace `k8s-ns`
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would be registered into Consul with the name `foo-k8s-ns`.
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This is useful when syncing from multiple Kubernetes namespaces to
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a single Consul namespace. However, you may want to disable this behavior
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when mirroring namespaces so that services do not overlap with services from
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other namespaces.
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## Consul to Kubernetes
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This syncs Consul services into first-class Kubernetes services.
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The sync creates an [`ExternalName`](https://kubernetes.io/docs/concepts/services-networking/service/#externalname) for each Consul service. The "external name" is the Consul DNS name.
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For example, given a Consul service `foo`:
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```yaml
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apiVersion: v1
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kind: Service
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metadata:
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name: foo
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...
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spec:
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externalName: foo.service.consul
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type: ExternalName
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```
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With Consul To Kubernetes syncing enabled, DNS requests of the form `<consul-service-name>`
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are serviced by Consul DNS. From a different Kubernetes namespace than where Consul
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is deployed, the DNS request would need to be `<consul-service-name>.<consul-namespace>`.
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-> **Note:** Consul to Kubernetes syncing is not required if you enabled [Consul DNS on Kubernetes](/consul/docs/k8s/dns).
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All you need to do is address services in the form `<consul-service-name>.service.consul`, so you do not need Kubernetes `Service` objects created.
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~> **Requires Consul DNS via CoreDNS in Kubernetes:** This feature requires that
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[Consul DNS](/consul/docs/k8s/dns) 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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### Enable and disable sync
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All Consul services visible to the sync process based on its given ACL token
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are 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 matches the name of the Consul service exactly.
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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 is not 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 cannott 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 are labeled and annotated.
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An annotation `consul.hashicorp.com/synced` is 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` is 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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