During a deployment the orchestrator performs some operations on the containers. To see the operations, we can make use of some commands which paints a clear picture on series of steps taken to reach the goal. The two main commands are logs and describe.
If you have followed the previous part till end then you can run the following commands else follow steps to create replica sets.
Log
If we use the log command to inspect the deployment we created my-apache,
kubectl logs deploy/my-apache
it spits out the following on the terminal.
Found 2 pods, using pod/my-apache-5d589d69c7-mb7wx
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.3. Set the 'ServerName' directive globally to suppress this message
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.3. Set the 'ServerName' directive globally to suppress this message
[Thu Nov 21 14:23:27.128189 2019] [mpm_event:notice] [pid 1:tid 139734356759680] AH00489: Apache/2.4.41 (Unix) configured -- resuming normal operations
[Thu Nov 21 14:23:27.150818 2019] [core:notice] [pid 1:tid 139734356759680] AH00094: Command line: 'httpd -D FOREGROUND'
Inorder to inspect the pods based on some label, we can use the command
kubectl logs -l run=my-apache
here -l is for label and when we created the replica sets for my-apache, by default
a label is associated with the pods with the name of the cluster.
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.6. Set the 'ServerName' directive globally to suppress this message
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.6. Set the 'ServerName' directive globally to suppress this message
[Sun Nov 24 23:15:59.252042 2019] [mpm_event:notice] [pid 1:tid 140337709847680] AH00489: Apache/2.4.41 (Unix) configured -- resuming normal operations
[Sun Nov 24 23:15:59.252156 2019] [core:notice] [pid 1:tid 140337709847680] AH00094: Command line: 'httpd -D FOREGROUND'
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.5. Set the 'ServerName' directive globally to suppress this message
AH00558: httpd: Could not reliably determine the server's fully qualified domain name, using 10.1.10.5. Set the 'ServerName' directive globally to suppress this message
[Sun Nov 24 23:15:08.958846 2019] [mpm_event:notice] [pid 1:tid 140277681194112] AH00489: Apache/2.4.41 (Unix) configured -- resuming normal operations
[Sun Nov 24 23:15:08.959020 2019] [core:notice] [pid 1:tid 140277681194112] AH00094: Command line: 'httpd -D FOREGROUND'
What’s to note here is logging using kubernetes built in commands is fine for few pods. However we should consider using a thrid party system for better logging as using the built-in commands is taxing after a few pods. This is infact true for a number of container orchestration tools present out there.
describe
The second way to inspect objects is with the describe command.
As is evident from the name itself, the describe command gives a very detailed inspection.
To inspect a pod we can use the command
kubectl describe pod/<pod-name>
we can find the names of the pods running with command
kubectl get pods
This gives a very detailed description about the pod, containers present, conditions and events.
One nice feature is to use the watch feature.
This one gives us a running log for all the operations being performed.
To use this you can use the command
kubectl get pods -w
NAME READY STATUS RESTARTS AGE
my-apache-5d589d69c7-4p8qd 1/1 Running 0 46m
my-apache-5d589d69c7-jz6nc 1/1 Running 0 47m
It will return the following and let’s say if you add a new replica or delete an existing pod, then you can see the running log. Try deleting one of the pods with the command
kubectl delete pod/my-apache-5d589d69c7-4p8qd
and you can see the changes happening.