Running the demo in a docker container (on a Linux x64/aarch64 machine)

Description

The crac8 demo should emulate a service that needs to load around 258 000 names from a json file at startup. The "service" provides methods to create a number of random names for either boys or girls. When started normally it will first load the data from the json file into datastructures and then will create 5 random names for girls and 5 random names for boys. This will take around 1-2 sec depending on the machine you run it on. Once you create a checkpoint and restore it from there, the response will only take around 30-50 ms because the data was already loaded from the file and now one can directly access it which leads to the fast "startup" time.

Build the jar file on the target platform:

To create the jar file you need to build it on the target platform (Linux x64 or aarch64) using the a JDK that supports CRaC. You can find builds here Azul.

1. make sure you set JAVA_HOME to the JVM with CRaC support
2. go the project folder
3. run gradlew clean build
4. Now you should find the the jar at build/libs/crac8-17.0.0-fat.jar
5. This jar file will later be used to run on the docker container
6. Make sure to select the correct JDK in the docker file (x64 or aarch64)

Login into docker:

docker login

Build docker image:

docker build -t crac8 .

Commit image to dockerhub:

docker commit crac8

Run docker image without checkpoint:

docker run -it --privileged --rm --name crac8 hansolo/crac8 java -XX:CRaCCheckpointTo=/opt/crac-files -jar /opt/app/crac8-17.0.0.jar

Run docker image with checkpoint:

docker run -it --privileged --rm --name $1 hansolo/crac8:checkpoint java -XX:CRaCRestoreFrom=/opt/crac-files

1. Start the application in a docker container

1. Open a shell window
2. Run docker run -it --privileged --rm --name crac8 crac8
3. In the docker container run
   

cd /opt/app
java -XX:CRaCCheckpointTo=/opt/crac-files -jar crac8-17.0.0.jar keeprunning

2. Start a 2nd shell window and create the checkpoint

1. Open a second shell window
2. Run docker exec -it -u root crac8 /bin/bash
3. Execute top command and note the PID of the running java process
4. Take the PID and run jcmd PID JDK.checkpoint
5. In the first shell window the application should have created the checkpoint
6. Check the folder /opt/crac-files for the checkpoint files being present
7. In second shell window run exit to get back to your machine

3. Commit the current state of the docker container

1. Now get the CONTAINER_ID from shell window 1 by execute docker ps -a in shell window 2
2. Exit the docker container in shell window 1 by executing exit
3. Run docker commit CONTAINER_ID crac8:checkpoint in shell window 2

4. Run the docker container from the saved state incl. the checkpoint

Now you can start the docker container from the checkpoint by executing docker run -it --privileged --rm --name crac8 crac8:checkpoint java -XX:CRaCRestoreFrom=/opt/crac-files

5. Create a shell script to restore multiple times

1. Open a shell window
2. Create a text file named restore_crac8.sh
3. Add

#!/bin/bash

echo "docker run -it --privileged --rm --name $1 crac8:checkpoint java -XX:CRaCRestoreFrom=/opt/crac-files"

docker run -it --privileged --rm --name $1 crac8:checkpoint java -XX:CRaCRestoreFrom=/opt/crac-files

4. Make the script executable by executing chmod +x restore_crac8.sh
5. Now you can start the docker container multiple times executing restore_crac8.sh NAME_OF_CONTAINER

If you would like to start the original container without the checkpoint you can still do that by executing the following command

docker run -it --privileged --rm --name crac8 crac8 java -jar /opt/app/crac8-17.0.0.jar