whentimeslows/website
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Re-organize doc

Browse Source
This commit is contained in:
lucperkins
2018-06-20 22:12:01 -07:00
parent 472be9a374
commit 5391d054e4
1 changed files with 71 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files
content/en/docs/concepts/services-networking/service.md
+71 -36
View File
@@ -135,32 +135,15 @@ The traffic will be routed to endpoints defined by the user (`1.2.3.4:9376` in
this example).
An ExternalName service is a special case of service that does not have
selectors. It does not define any ports or Endpoints. Rather, it serves as a
way to return an alias to an external service residing outside the cluster.
```yaml
kind: Service
apiVersion: v1
metadata:
name: my-service
namespace: prod
spec:
type: ExternalName
externalName: my.database.example.com
```
When looking up the host `my-service.prod.svc.CLUSTER`, the cluster DNS service
will return a `CNAME` record with the value `my.database.example.com`. Accessing
such a service works in the same way as others, with the only difference that
the redirection happens at the DNS level and no proxying or forwarding occurs.
Should you later decide to move your database into your cluster, you can start
its pods, add appropriate selectors or endpoints and change the service `type`.
selectors and uses DNS names instead. For more information, see the
[ExternalName](#externalname) section later in this document.
## Virtual IPs and service proxies
Every node in a Kubernetes cluster runs a `kube-proxy`. `kube-proxy` is
Every node in a Kubernetes cluster runs a `kube-proxy`. `kube-proxy` is
responsible for implementing a form of virtual IP for `Services` of type other
than `ExternalName`.
than [`ExternalName`](#externalname).
In Kubernetes v1.0, `Services` are a "layer 4" (TCP/UDP over IP) construct, the
proxy was purely in userspace. In Kubernetes v1.1, the `Ingress` API was added
(beta) to represent "layer 7"(HTTP) services, iptables proxy was added too,
@@ -348,7 +331,8 @@ can do a DNS SRV query for `"_http._tcp.my-service.my-ns"` to discover the port
number for `"http"`.
The Kubernetes DNS server is the only way to access services of type
`ExternalName`. More information is available in the [DNS Pods and Services](/docs/concepts/services-networking/dns-pod-service/).
`ExternalName`. More information is available in the [DNS Pods and
Services](/docs/concepts/services-networking/dns-pod-service/).
## Headless services
@@ -378,7 +362,7 @@ For headless services that do not define selectors, the endpoints controller doe
not create `Endpoints` records. However, the DNS system looks for and configures
either:
* CNAME records for `ExternalName`-type services.
* CNAME records for [`ExternalName`](#externalname)-type services.
* A records for any `Endpoints` that share a name with the service, for all
other types.
@@ -396,19 +380,20 @@ The default is `ClusterIP`.
* `ClusterIP`: Exposes the service on a cluster-internal IP. Choosing this value
makes the service only reachable from within the cluster. This is the
default `ServiceType`.
* `NodePort`: Exposes the service on each Node's IP at a static port (the `NodePort`).
A `ClusterIP` service, to which the `NodePort` service will route, is automatically
created. You'll be able to contact the `NodePort` service, from outside the cluster,
* [`NodePort`](#nodeport): Exposes the service on each Node's IP at a static port
(the `NodePort`). A `ClusterIP` service, to which the `NodePort` service will
route, is automatically created. You'll be able to contact the `NodePort` service,
from outside the cluster,
by requesting `<NodeIP>:<NodePort>`.
* `LoadBalancer`: Exposes the service externally using a cloud provider's load balancer.
`NodePort` and `ClusterIP` services, to which the external load balancer will route,
are automatically created.
* `ExternalName`: Maps the service to the contents of the `externalName` field
(e.g. `foo.bar.example.com`), by returning a `CNAME` record with its value.
No proxying of any kind is set up. This requires version 1.7 or higher of
`kube-dns`.
* [`LoadBalancer`](#loadbalancer): Exposes the service externally using a cloud
provider's load balancer. `NodePort` and `ClusterIP` services, to which the external
load balancer will route, are automatically created.
* [`ExternalName`](#externalname): Maps the service to the contents of the
`externalName` field (e.g. `foo.bar.example.com`), by returning a `CNAME` record
with its value. No proxying of any kind is set up. This requires version 1.7 or
higher of `kube-dns`.
### Type NodePort
### Type NodePort {#nodeport}
If you set the `type` field to `NodePort`, the Kubernetes master will
allocate a port from a range specified by `--service-node-port-range` flag (default: 30000-32767), and each
@@ -429,7 +414,7 @@ even to just expose one or more nodes' IPs directly.
Note that this Service will be visible as both `<NodeIP>:spec.ports[*].nodePort`
and `.spec.clusterIP:spec.ports[*].port`. (If the `--nodeport-addresses` flag in kube-proxy is set, <NodeIP> would be filtered NodeIP(s).)
### Type LoadBalancer
### Type LoadBalancer {#loadbalancer}
On cloud providers which support external load balancers, setting the `type`
field to `LoadBalancer` will provision a load balancer for your `Service`.
@@ -756,6 +741,56 @@ spec:
**Note:** NLB only works with certain instance classes, see the [AWS documentation](http://docs.aws.amazon.com/elasticloadbalancing/latest/network/target-group-register-targets.html#register-deregister-targets)
for supported instance types.
### Type ExternalName {#externalname}
{{< note >}}
ExternalName Services are available only with `kube-dns` version 1.7 and later.
{{< /note >}}
Services of type ExternalName map a service to a DNS name (specified using
the `spec.externalName` parameter) rather than to a typical selector like
`my-service` or `cassandra`. This Service definition, for example, would map
the `my-service` Service in the `prod` namespace to `my.database.example.com`:
```yaml
kind: Service
apiVersion: v1
metadata:
name: my-service
namespace: prod
spec:
type: ExternalName
externalName: my.database.example.com
```
When looking up the host `my-service.prod.svc.CLUSTER`, the cluster DNS service
will return a `CNAME` record with the value `my.database.example.com`. Accessing
`my-service` works in the same way as other Services but with the crucial
difference that redirection happens at the DNS level rather than via proxying or
forwarding. Should you later decide to move your database into your cluster, you
can start its pods, add appropriate selectors or endpoints and change the service `type`.
#### Using ExternalName Services across namespaces
In addition to enabling Kubernetes pods to
```yaml
kind: Service
apiVersion: v1
metadata:
name: my-service
namespace: namespace-a
spec:
type: ExternalName
externalName: my-service.namespace-b.svc.cluster.local
ports:
- port: 80
```
{{< note >}}
This section is indebted to the [Kubernetes Tips - Part
1](https://akomljen.com/kubernetes-tips-part-1/) blog post from [Alen Komljen](https://akomljen.com/).
{{< /note >}}
### External IPs