Django migrations with Docker on AWS Elastic Beanstalk - amazon-web-services

Question

I have a django app running inside a single docker container on AWS Elastic Beanstalk. I cannot get it to run migrations properly, it always sees the old docker image and tries to run migrations from that (but it doesn’t have the latest files).
I package an .ebextensions directory with my EBS source bundle (a zip containing a Dockerrun.aws.json file and the .ebextensions dir). And it has a setup.config file that looks like this:
container_commands:
01_migrate:
command: "CONTAINER=`docker ps -a --no-trunc | grep aws_beanstalk | cut -d' ' -f1 | head -1` && docker exec $CONTAINER python3 manage.py migrate"
leader_only: true
Which is partially modeled after the comments on this SO question.
I have verified that it can work if I simply re-deploy the app a second time, since this time the previous running image will have the updated migrations file.
Does anyone know how to access the latest docker image or latest running container in an .ebextensions script?

Answer 1

Based on AWS Documentation on Customizing Software on Linux Servers, container_commands will be executed before your app is deployed.
You can use the container_commands key to execute commands for your container. The commands in container_commands are processed in alphabetical order by name. They run after the application and web server have been set up and the application version file has been extracted, but before the application version is deployed. They also have access to environment variables such as your AWS security credentials. Additionally, you can use leader_only. One instance is chosen to be the leader in an Auto Scaling group. If the leader_only value is set to true, the command runs only on the instance that is marked as the leader.
Take a look also into my answer in here. It run some command in different app deployment state and give the command result.
So, your problem solution might be create an post app deployment hook.
.ebextensions/00_post_migrate.config
files:
"/opt/elasticbeanstalk/hooks/appdeploy/post/10_post_migrate.sh":
mode: "000755"
owner: root
group: root
content: |
#!/usr/bin/env bash
if [ -f /tmp/leader_only ]
then
rm /tmp/leader_only
docker exec `docker ps --no-trunc -q | head -n 1` python3 manage.py migrate
fi
container_commands:
01_migrate:
command: "touch /tmp/leader_only"
leader_only: true

Answer 2

I am using another approach. What I did is run a container based on the newly build image, then pass in the environment variables from Elastic Beanstalk and run the custom command in that container. When that command is done, it will remove itself and proceed with the deployment.
So this is the script I have put inside .ebextensions/scripts/container_command.sh (make sure you replace everything that is within <>):
#!/bin/bash
COMMAND=$1
EB_CONFIG_DOCKER_IMAGE_STAGING=$(/opt/elasticbeanstalk/bin/get-config container -k <environment_name>_image)
EB_SUPPORT_FILES=$(/opt/elasticbeanstalk/bin/get-config container -k support_files_dir)
# build --env arguments for docker from env var settings
EB_CONFIG_DOCKER_ENV_ARGS=()
while read -r ENV_VAR; do
EB_CONFIG_DOCKER_ENV_ARGS+=(--env "${ENV_VAR}")
done < <($EB_SUPPORT_FILES/generate_env)
docker run --name=shopblender_pre_deploy -d \
"${EB_CONFIG_DOCKER_ENV_ARGS[#]}" \
"${EB_CONFIG_DOCKER_IMAGE_STAGING}"
docker exec shopblender_pre_deploy ${COMMAND}
# clean up
docker stop shopblender_pre_deploy
docker rm shopblender_pre_deploy
Now, you can use this script to execute any custom command to the container that will be deployed later.
Something like this .ebextensions/container_commands.config:
container_commands:
01-command:
command: bash .ebextensions/scripts/container_command.sh "php app/console doctrine:schema:update --force --no-interaction" &>> /var/log/database.log
leader_only: true
02-command:
command: bash .ebextensions/scripts/container_command.sh "php app/console fos:elastica:reset --no-interaction" &>> /var/log/database.log
leader_only: true
03-command:
command: bash .ebextensions/scripts/container_command.sh "php app/console doctrine:fixtures:load --no-interaction" &>> /var/log/database.log
leader_only: true
This way you also do not need to worry about what your latest started container is, which is a problem with the solution described above.