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