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()

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2. Create a container with the following definition:

   # cat Containerfile
   FROM registry.access.redhat.com/ubi8/ubi
   
   COPY counter.py /home/counter.py
   
   RUN useradd -ms /bin/bash counter
   
   RUN yum -y install python3 && chmod 755 /home/counter.py
   
   USER counter
   ENTRYPOINT /home/counter.py

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   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

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   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

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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

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6. Display IP address of the container:

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

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7. Send requests to the container:

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

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8. Create a checkpoint for the container:

   # podman container checkpoint criu-test

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9. Reboot the system.

10. Restore the container:

    # podman container restore --keep criu-test

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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

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    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

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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

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   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

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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

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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

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   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

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2. Display IP address of the container:

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

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3. Send requests to the container:

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

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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

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5. Copy the checkpoint archive to the destination host:

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

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

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

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

   # *curl 10.88.0.247:8080*
   2

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