# 4. Observability (18%)
### Defining a Pod’s Readiness and Liveness Probe
1. Create a new Pod named `hello` with the image `bonomat/nodejs-hello-world` that exposes the port `3000`. Provide the name `nodejs-port` for the container port.
2. Add a `Readiness Probe` that checks the URL path `/` on the port referenced with the name `nodejs-port` after a 2 seconds delay. You do not have to define the period interval.
3. Add a `Liveness Probe` that verifies that the app is up and running every 8 seconds by checking the URL path / on the port referenced with the name `nodejs-port`. The probe should start with a 5 seconds delay.
4. Shell into container and curl `localhost:3000`. Write down the output. Exit the container. Retrieve the logs from the container. Write down the output.
答案：\
Create the intial YAML with the following command.
```
$ kubectl run hello --image=bonomat/nodejs-hello-world --restart=Never --port=3000 -o yaml --dry-run > pod.yaml
```
Edit the YAML file and add the probes.\
参考官网： [livenessProbe](https://kubernetes.io/zh/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/)
```
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: hello
name: hello
spec:
containers:
- image: bonomat/nodejs-hello-world
name: hello
ports:
- name: nodejs-port
containerPort: 3000
readinessProbe:
httpGet:
path: /
port: nodejs-port
initialDelaySeconds: 2
livenessProbe:
httpGet:
path: /
port: nodejs-port
initialDelaySeconds: 5
periodSeconds: 8
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Never
status: {}
```
Create the Pod from the YAML file, shell into the Pod as soon as it is running and execute the curl command.
```
$ kubectl create -f pod.yaml
pod/hello created
$ kubectl exec hello -it -- /bin/sh
/ # curl localhost:3000
NodeJS Docker Hello World
This is just a hello world message
/ # exit
$ kubectl logs pod/hello
Magic happens on port 3000
```
### Fixing a Misconfigured Pod
1. Create a new Pod with the following YAML.
```
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: failing-pod
name: failing-pod
spec:
containers:
- args:
- /bin/sh
- -c
- while true; do echo $(date) >> ~/tmp/curr-date.txt; sleep
5; done;
image: busybox
name: failing-pod
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Never
status: {}
```
1. Check the Pod’s status. Do you see any issue?
2. Follow the logs of the running container and identify an issue.
3. Fix the issue by shelling into the container. After resolving the issue the current date should be written to a file. Render the output.
答案：\
First, create the Pod with the given YAML content.
```
$ vim pod.yaml
$ kubectl create -f pod.yaml
```
The Pod seems to be running without problems.
```
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
failing-pod 1/1 Running 0 5s
```
Render the logs of the container. The output should indicate an error message every 5 seconds.
```
$ kubectl logs failing-pod
Unable to write file!
/bin/sh: 1: cannot create /root/tmp/curr-date.txt: Directory nonexistent
Unable to write file!
/bin/sh: 1: cannot create /root/tmp/curr-date.txt: Directory nonexistent
Unable to write file!
/bin/sh: 1: cannot create /root/tmp/curr-date.txt: Directory nonexistent
```
Apparently, the directory we want to write to does not exist. Log into the container and create the directory. The file `~/tmp/curr-date.txt` is populated.
```
$ kubectl exec failing-pod -it -- /bin/sh
/ # mkdir -p ~/tmp
/ # cd ~/tmp
/ # ls -l
total 4
-rw-r--r-- 1 root root 112 May 9 23:52 curr-date.txt
/ # cat ~/tmp/curr-date.txt
Thu May 9 23:59:01 UTC 2019
Thu May 9 23:59:06 UTC 2019
Thu May 9 23:59:11 UTC 2019
/ # exit
```
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