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Tweak job-with-pod-to-pod-communication.md

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@ -7,20 +7,21 @@ weight: 30
<!-- overview --> <!-- overview -->
In this example, you will run a Job in [Indexed completion mode](/blog/2021/04/19/introducing-indexed-jobs/) configured such that In this example, you will run a Job in [Indexed completion mode](/blog/2021/04/19/introducing-indexed-jobs/)
the pods created by the Job can communicate with each other using pod hostnames rather than pod IP addresses. configured such that the pods created by the Job can communicate with each other using pod hostnames rather
than pod IP addresses.
Pods within a Job might need to communicate among themselves. The user workload running in each pod could query the Kubernetes API server Pods within a Job might need to communicate among themselves. The user workload running in each pod
to learn the IPs of the other Pods, but it's much simpler to rely on Kubernetes' built-in DNS resolution. could query the Kubernetes API server to learn the IPs of the other Pods, but it's much simpler to
rely on Kubernetes' built-in DNS resolution.
Jobs in Indexed completion mode automatically set the pods' hostname to be in the format of Jobs in Indexed completion mode automatically set the pods' hostname to be in the format of
`${jobName}-${completionIndex}`. You can use this format to deterministically build `${jobName}-${completionIndex}`. You can use this format to deterministically build
pod hostnames and enable pod communication *without* needing to create a client connection to pod hostnames and enable pod communication *without* needing to create a client connection to
the Kubernetes control plane to obtain pod hostnames/IPs via API requests. the Kubernetes control plane to obtain pod hostnames/IPs via API requests.
This configuration is useful This configuration is useful for use cases where pod networking is required but you don't want
for use cases where pod networking is required but you don't want to depend on a network to depend on a network connection with the Kubernetes API server.
connection with the Kubernetes API server.
## {{% heading "prerequisites" %}} ## {{% heading "prerequisites" %}}
@ -28,40 +29,43 @@ You should already be familiar with the basic use of [Job](/docs/concepts/worklo
{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}} {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
{{<note>}} {{< note >}}
If you are using MiniKube or a similar tool, you may need to take If you are using minikube or a similar tool, you may need to take
[extra steps](https://minikube.sigs.k8s.io/docs/handbook/addons/ingress-dns/) [extra steps](https://minikube.sigs.k8s.io/docs/handbook/addons/ingress-dns/)
to ensure you have DNS. to ensure you have DNS.
{{</note>}} {{< /note >}}
<!-- steps --> <!-- steps -->
## Starting a Job with Pod-to-Pod Communication ## Starting a Job with pod-to-pod communication
To enable pod-to-pod communication using pod hostnames in a Job, you must do the following: To enable pod-to-pod communication using pod hostnames in a Job, you must do the following:
1. Set up a [headless Service](/docs/concepts/services-networking/service/#headless-services) 1. Set up a [headless Service](/docs/concepts/services-networking/service/#headless-services)
with a valid label selector for the pods created by your Job. The headless service must be in the same namespace as with a valid label selector for the pods created by your Job. The headless service must be
the Job. One easy way to do this is to use the `job-name: <your-job-name>` selector, since the `job-name` label will be automatically added by Kubernetes. This configuration will trigger the DNS system to create records of the hostnames of in the same namespace as the Job. One easy way to do this is to use the
the pods running your Job. `job-name: <your-job-name>` selector, since the `job-name` label will be automatically added
by Kubernetes. This configuration will trigger the DNS system to create records of the hostnames
of the pods running your Job.
2. Configure the headless service as subdomain service for the Job pods by including the following value in your Job template spec: 1. Configure the headless service as subdomain service for the Job pods by including the following
value in your Job template spec:
```yaml ```yaml
subdomain: <headless-svc-name> subdomain: <headless-svc-name>
``` ```
### Example ### Example
Below is a working example of a Job with pod-to-pod communication via pod hostnames enabled. Below is a working example of a Job with pod-to-pod communication via pod hostnames enabled.
The Job is completed only after all pods successfully ping each other using hostnames. The Job is completed only after all pods successfully ping each other using hostnames.
{{<note>}} {{< note >}}
In the Bash script executed on each pod in the example below, the pod hostnames can be prefixed In the Bash script executed on each pod in the example below, the pod hostnames can be prefixed
by the namespace as well if the pod needs to be reached from outside the namespace. by the namespace as well if the pod needs to be reached from outside the namespace.
{{</note>}} {{< /note >}}
```yaml ```yaml
apiVersion: v1 apiVersion: v1
kind: Service kind: Service
metadata: metadata:
@ -121,8 +125,8 @@ Successfully pinged pod: example-job-1.headless-svc
Successfully pinged pod: example-job-2.headless-svc Successfully pinged pod: example-job-2.headless-svc
``` ```
{{<note>}} {{< note >}}
Keep in mind that the `<pod-hostname>.<headless-service-name>` name format used Keep in mind that the `<pod-hostname>.<headless-service-name>` name format used
in this example would not work with DNS policy set to `None` or `Default`. in this example would not work with DNS policy set to `None` or `Default`.
You can learn more about pod DNS policies [here](/docs/concepts/services-networking/dns-pod-service/#pod-s-dns-policy). Refer to [Pod's DNS Policy](/docs/concepts/services-networking/dns-pod-service/#pod-s-dns-policy).
{{</note>}} {{< /note >}}