Merge pull request flashreads#162 from natemago/article-read-kubernet…

…es-job-logs

Adds article on how to read kubernetes job logs.

kubernetes/001-kubernetes-job-logs.md

@@ -0,0 +1,107 @@
+---
+id: 001-kubernetes-job-logs.md
+title: Show Kubernetes Job Logs
+tags: 
+    - kubernetes
+    - kubectl
+    - kubernetes-job
+    - logs
+    - cli
+date: 2020-10-13 17:50:14 +0200 
+keywords: kubernetes, job, logs, read logs
+categories: kubernetes
+cover: ../../images/kubernetes.png
+author: Pavle Jonoski
+meta-description: Read logs of a kubernetes job
+---
+
+# Get Kubernetes Job Logs
+
+When using [Kubernetes](https://kubernetes.io/), often you need to read logs from the running pods.
+On a bigger cluster you may have many pods that are running and many that have either completed or errored out.
+When deploying [Kubernetes Jobs](https://kubernetes.io/docs/concepts/workloads/controllers/job/), often you want to read the logs of the job, whether it completed or has any errors.
+Finding the correct pod amongst many pods may be a bit of a challenge.
+
+In this post you'll learn how to list the correct job pods - all of them, and how to retrieve the job logs - from the current 
+completed pod and from a pods that exited with error.
+
+Given you already have a Kubernetes cluster, and the job was deployed in a namespace, this is what you want to do.
+
+## List the job pods
+Let's say we have a job like this:
+
+```yaml
+apiVersion: batch/v1
+kind: Job
+metadata:
+  name: calculate-fibonacci
+  namespace: example
+spec:
+  template:
+    spec:
+      containers:
+      - name: fibonacci
+        image: node:16-alpine
+        command: ['node',  '-e', 'function f(x){ if(x === 1 || x === 2) return 1; return f(x-1)+f(x-2);} console.log("The 10th fibonacci number is: ", f(10));']
+      restartPolicy: Never
+  backoffLimit: 4
+```
+
+The Job definition:
+ * The name of the job is `calculate-fibonacci`
+ * The job is in namespace called `example`
+
+
+To list the pods associated with this job, do:
+
+```bash
+kubectl -n example get pods -l job-name=calculate-fibonacci
+```
+
+* `-n example` - this tells `kubectl` to work in the `example` namespace
+* `get pods` will give us the list of pods in the namespace
+* `-l job-name=calculate-fibonacci` this refines the list of pods that have a label `job-name` with the name of our job: `calculate-fibonacci`
+
+This will produce the following output:
+```
+NAME                           READY   STATUS      RESTARTS   AGE
+calculate-fibonacci--1-pdzg4   0/1     Completed   0          3s
+```
+
+## Get the job logs
+
+Once we know the pods associated with a job, we can view the logs the same way we view the logs for any pod: `kubectl logs <the id of the pod>`:
+
+```bash
+kubectl -n example logs calculate-fibonacci--1-pdzg4
+```
+
+It will give us the logs for the job:
+
+```
+The 10th fibonacci number is:  55
+```
+
+If the job is still running and we want to follow the logs as they are printed out, just add `-f` (follow) to the command:
+
+```bash
+kubectl -n example logs -f calculate-fibonacci--1-pdzg4
+```
+## One-liner for viewing the logs of a completed job
+
+Now we can combine the both commands into a single one, to view the logs for a completed job:
+
+```bash
+kubectl -n example logs $(kubectl -n example get pods -l job-name=calculate-fibonacci --field-selector='status.phase=Succeeded' --no-headers -o custom-columns=':metadata.name')
+```
+
+It will give us the logs of the completed pod directly:
+
+```
+The 10th fibonacci number is:  55
+```
+
+Notice that we added a couple of things in the command that selects the pod:
+* `--field-selector='status.phase=Succeeded'` - we want to find the pod that has `Succeeded` status (everything went OK)
+* `--no-headers` - we don't want any headers in the output, as we only want the pod id
+* `custom-columns=':metadata.name'` - show just the `metadata.name` of the pod (the id)