Container Internals

Now let’s have a more in depth look at the running containers.

Container process inspection

Container top gives you the running processes inside a container. We can see that we have the node server running inside the container.

podman top k8sdemo

>USER        PID         PPID        %CPU        ELAPSED       TTY         TIME        COMMAND
>root        1           0           0.000       6.271110421s  ?           0s          npm
>root        12          1           0.000       6.271156588s  ?           0s          sh -c node ./bin/www
>root        13          12          0.000       6.271178838s  ?           0s          node ./bin/www```

Container inspect outputs the detailed configuration of the running container.

podman inspect k8sdemo

> [
>     {
>         "Id": "48f5cd2708b27da27b0edcc1aaa3b6308249e6de94d45c0b123bf5fc7f2efbbf",
>         "Created": "2020-05-19T08:48:03.867340977Z",
>         "Path": "podman-entrypoint.sh",
>         "Args": [
>             "npm",
>             "start"
>         ],

Container logs

In order to access the logs of the container (especially if it runs in the background with the -d option) you can use podman logs.

podman logs k8sdemo

> test@0.0.0 start /app
> node ./bin/www

Container exec

Container exec allows to run commands inside already running containers. This is very useful for debugging.

podman exec -it k8sdemo /bin/bash

You get a prompt inside the container. Now you can explore the content of the running container.

List the files in the home directory (execute at the container prompt)

ls -al

>total 52
>drwxr-xr-x. 1 root root   165 Apr 11 11:04 .
>dr-xr-xr-x. 1 root root    40 Apr 11 12:09 ..
>-rw-r--r--. 1 root root   496 Mar 29 09:08 Dockerfile
>-rw-r--r--. 1 root root    78 Mar 29 09:08 README
>-rw-r--r--. 1 root root  1226 Mar 29 09:08 app.js
>drwxr-xr-x. 2 root root    17 Mar 29 09:08 bin
>-rw-r--r--. 1 root root   306 Mar 29 09:08 build.sh
>drwxr-xr-x. 1 root root  4096 Mar 29 09:08 node_modules

List the web files for the node application (execute at the container prompt)

cd public/
ls -al

    > total 144
    > drwxrwxr-x 1 root root  4096 May 14 06:55 .
    > drwxr-xr-x 1 root root  4096 May 14 07:25 ..
    > -rw-rw-r-- 1 root root  6148 May 14 06:55 .DS_Store
    > -rw-rw-r-- 1 root root 32939 May 14 06:55 404.html
    > -rw-rw-r-- 1 root root 55515 May 14 06:55 500.html
    > drwxrwxr-x 2 root root  4096 May 14 06:55 images
    > -rwxrwxr-x 1 root root  6240 May 19 08:22 index.html
    > -rwxrwxr-x 1 root root  1188 May 14 06:55 index.js

Modify the HTML code for the running container (execute at the container prompt)

echo '<H1 style="background-color: #ff0000">HELLO</H1>' >> index.html

Reload the Web App and look for the HELLO text displayed in the lower left part of the page.
Type exit in order to get back to the commandline

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