Chapter 22. Creating and restoring container checkpoints

Procedure

1. Create a Python based server:

   # cat counter.py
   #!/usr/bin/python3
   
   import http.server
   
   counter = 0
   
   class handler(http.server.BaseHTTPRequestHandler):
       def do_GET(s):
           global counter
           s.send_response(200)
           s.send_header('Content-type', 'text/html')
           s.end_headers()
           s.wfile.write(b'%d\n' % counter)
           counter += 1
   
   
   server = http.server.HTTPServer(('', 8088), handler)
   server.serve_forever()

   Copy to Clipboard

2. Create a container with the following definition:

   # cat Containerfile
   FROM registry.access.redhat.com/ubi9/ubi
   
   COPY counter.py /home/counter.py
   
   RUN useradd -ms /bin/bash counter
   
   RUN dnf -y install python3 && chmod 755 /home/counter.py
   
   USER counter
   ENTRYPOINT /home/counter.py

   Copy to Clipboard

   The container is based on the Universal Base Image (UBI 8) and uses a Python based server.

3. Build the container:

   # podman build . --tag counter

   Copy to Clipboard

   Files counter.py and Containerfile are the input for the container build process (podman build). The built image is stored locally and tagged with the tag counter.

4. Start the container as root:

   # podman run --name criu-test --detach counter

   Copy to Clipboard

5. To list all running containers, enter:

   # podman ps
   CONTAINER ID  IMAGE  COMMAND  CREATED   STATUS  PORTS NAMES
   e4f82fd84d48  localhost/counter:latest  5 seconds ago  Up 4 seconds ago  criu-test

   Copy to Clipboard

6. Display IP address of the container:

   # podman inspect criu-test --format "{{.NetworkSettings.IPAddress}}"
   10.88.0.247

   Copy to Clipboard

7. Send requests to the container:

   # curl 10.88.0.247:8088
   0
   # curl 10.88.0.247:8088
   1

   Copy to Clipboard

8. Create a checkpoint for the container:

   # podman container checkpoint criu-test

   Copy to Clipboard
9. Reboot the system.

10. Restore the container:

    # podman container restore --keep criu-test

    Copy to Clipboard

11. Send requests to the container:

    # curl 10.88.0.247:8080
    2
    # curl 10.88.0.247:8080
    3
    # curl 10.88.0.247:8080
    4

    Copy to Clipboard

    The result now does not start at 0 again, but continues at the previous value.

Procedure

1. Create a checkpoint of the container, and export the checkpoint image to a tar.gz file:

   # podman container checkpoint criu-test --export /tmp/chkpt.tar.gz

   Copy to Clipboard

2. Restore the container from the tar.gz file:

   # podman container restore --import /tmp/chkpt.tar.gz --name counter1
   # podman container restore --import /tmp/chkpt.tar.gz --name counter2
   # podman container restore --import /tmp/chkpt.tar.gz --name counter3

   Copy to Clipboard

   The --name (-n) option specifies a new name for containers restored from the exported checkpoint.

3. Display ID and name of each container:

   # podman ps -a --format "{{.ID}} {{.Names}}"
   a8b2e50d463c counter3
   faabc5c27362 counter2
   2ce648af11e5 counter1

   Copy to Clipboard

4. Display IP address of each container:

   #️ podman inspect counter1 --format "{{.NetworkSettings.IPAddress}}"
   10.88.0.248
   
   #️ podman inspect counter2 --format "{{.NetworkSettings.IPAddress}}"
   10.88.0.249
   
   #️ podman inspect counter3 --format "{{.NetworkSettings.IPAddress}}"
   10.88.0.250

   Copy to Clipboard

5. Send requests to each container:

   #️ curl 10.88.0.248:8080
   4
   #️ curl 10.88.0.249:8080
   4
   #️ curl 10.88.0.250:8080
   4

   Copy to Clipboard

   Note, that the result is 4 in all cases, because you are working with different containers restored from the same checkpoint.

Procedure

1. Start the container as root:

   # podman run --name criu-test --detach counter

   Copy to Clipboard

2. Display IP address of the container:

   # podman inspect criu-test --format "{{.NetworkSettings.IPAddress}}"
   10.88.0.247

   Copy to Clipboard

3. Send requests to the container:

   # curl 10.88.0.247:8080
   0
   # curl 10.88.0.247:8080
   1

   Copy to Clipboard

4. Create a checkpoint of the container, and export the checkpoint image to a tar.gz file:

   # podman container checkpoint criu-test --export /tmp/chkpt.tar.gz

   Copy to Clipboard

5. Copy the checkpoint archive to the destination host:

   # scp /tmp/chkpt.tar.gz other_host:/tmp/

   Copy to Clipboard

6. Restore the checkpoint on the destination host (other_host):

   # podman container restore --import /tmp/chkpt.tar.gz

   Copy to Clipboard

7. Send a request to the container on the destination host (other_host):

   # *curl 10.88.0.247:8080*
   2

   Copy to Clipboard