Exec into the containers¶
If you want to examine the contents of a container “in place” using remote access to it, you can use the kubectl exec
command. It allows you to run any command or just open an interactive shell session in the container. Of course, you can have shell access to the container only if container supports it and has a “Running” state.
In the following examples we will access the container pxc
of the cluster1-pxc-0
Pod.
-
Run
date
command:$ kubectl exec -ti cluster1-pxc-0 -c pxc -- date
Expected output
Thu Nov 24 10:01:17 UTC 2022
You will see an error if the command is not present in a container. For example, trying to run the
time
command, which is not present in the container, by executingkubectl exec -ti cluster1-pxc-0 -c pxc -- time
would show the following result:error: Internal error occurred: error executing command in container: failed to exec in container: failed to start exec "71bdb96a65af89d3672cd0d69a8f2c1068542a97b1938e7f6f17d29a87d76453": OCI runtime exec failed: exec failed: unable to start container process: exec: "time": executable file not found in $PATH: unknown
-
Print
/var/log/mysqld.log
file to a terminal:$ kubectl exec -ti cluster1-pxc-0 -c pxc -- cat /var/log/mysqld.log
-
Similarly, opening an Interactive terminal, executing a pair of commands in the container, and exiting it may look as follows:
$ kubectl exec -ti cluster1-pxc-0 -c pxc -- bash bash-4.4$ hostname cluster1-pxc-0 bash-4.4$ ls /var/log/mysqld.log /var/log/mysqld.log bash-4.4$ exit exit $
Avoid the restart-on-fail loop for Percona XtraDB Cluster containers¶
The restart-on-fail loop takes place when the container entry point fails
(e.g. mysqld
crashes). In such a situation, Pod is continuously restarting.
Continuous restarts prevent to get console access to the container, and so a
special approach is needed to make fixes.
You can prevent such infinite boot loop by putting the Percona XtraDB Cluster
containers into the infinity loop without starting mysqld. This behavior
of the container entry point is triggered by the presence of the
/var/lib/mysql/sleep-forever
file.
For example, you can do it for the pxc
container of an appropriate Percona
XtraDB Cluster instance as follows:
$ kubectl exec -it cluster1-pxc-0 -c pxc -- sh -c 'touch /var/lib/mysql/sleep-forever'
If pxc
container can’t start, you can use logs
container instead:
$ kubectl exec -it cluster1-pxc-0 -c logs -- sh -c 'touch /var/lib/mysql/sleep-forever'
The instance will restart automatically and run in its usual way as soon as you
remove this file (you can do it with a command similar to the one you have used
to create the file, just substitute touch
to rm
in it).