A container that has a daemon that does nothing more than use a cron job to log output every second by default, or according to the interval declared in the env var DUMBDAEMON_EMISSION_INTERVAL.
DUMBDAEMON_STOOGE
The name of the stooge that will be emitted in the log output.
You can assign a known stooge such as moe, larry or curly, or you can make one up to suit your very particular need. The default value is UNKNOWN
DUMBDAEMON_EMISSION_INTERVAL
A string that describes the interval at which to emit a log entry. Use standard cron format notation.
The default value is * * * * * *.
Go the Katacoda Kubernete Playbround here.
Clone this source code into the Katacoda Kubernetes Playground
git clone https://github.com/reselbob/dumbdaemon.git
Navigate to the source code directory:
cd dumbdaemon
Apply the following manifest to attempt to create the daemonset.
kubectl apply -f k8s/daemonset.yaml
Now, see if any pods are running
kubectl get pods
You should see a response:
No resources found.
Also, take a fast look at the daemonset:
kubectl get ds
Notice from the result below that the daemonset exists but that nothing is running. Also notice that the
daemonset has a node selector, stooge=moe .
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
dumb-daemonset 0 0 0 0 0 stooge=moe 38s
Why aren't things working? Take a look at the manifest for the daemonset:
cat k8s/daemonset.yaml
Notice that the container has an attribute, nodeSelector set to stooge:moe.
When you run, kubectl describe node node01 you'll observe that node01 has no label stooge=moe.
So, let's add the label to the node.
kubectl label node node01 stooge=moe.
Now, take another look at the daemonset:
kubectl get ds
Here's the result. The daemonset is indeed running because the label has been added to the node.
NAME DESIRED CURRENT READY UP-TO-DATE AVAILABLE NODE SELECTOR AGE
dumb-daemonset 1 1 0 1 0 stooge=moe 9m7s
Next, let take a look at the logs from the daemonset's container. Get the pod name:
kubectl get pods
Then look at the logs.
kubectl logs -l name=dumbdaemon
You'll see output similar to the following:
{ stooge: 'moe', emitTime: 2019-08-27T21:28:11.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:12.002Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:13.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:14.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:15.002Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:16.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:17.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:18.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:19.001Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:20.002Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:21.003Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:22.003Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:23.002Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:24.002Z }
{ stooge: 'moe', emitTime: 2019-08-27T21:28:25.002Z }
The daemonset has been successfully installed and is operational.
Congratulations! Now, go buy yourself an ice cream cone!