How did docker compose down update the running image?

Question

I'm running an application with docker compose.

version: '3.8'
services:
  php:
    build:
      context: .
    ports:
      - "[::1]:${BACKEND_PORT}:80"
  frontend:
    build:
      context: .
      dockerfile: Dockerfile.frontend
    ports:
      - "[::1]:${FRONTEND_PORT}:80"

Whenever I change the source code I redeploy the application with docker compose up --build -d --remove-orphans and I am relatively sure that it often works.

I just had a situation where the deploy didn't work, it would continue to run the old code. Come to think of it, I had this happen in the past but I never paid much attention and just continued making changes and re-deploying and in the end it always worked.

But this time there was only one change that I wanted to deploy and this time I'm absolutely sure that docker compose up --build -d --remove-orphans did not correctly re-deploy the application. I ran it several times, cleared client-side caches, etc.

I then ran docker compose down --remove-orphans followed by docker compose up --build -d --remove-orphans and finally the application got deployed correctly.

Is docker compose up --build -d --remove-orphans not enough to re-build the image and run it?

Answer 1

Redeploying with docker-compose up --build -d --remove-orphans did not correctly deploy the updated code, due to the caching during the build process to speed up subsequent builds. This could lead to situations where changes in your source code are not reflected in the built image because Docker is using the cached layers. Running docker-compose down --remove-orphans followed by docker-compose up --build -d --remove-orphans effectively forces Docker to start from a clean slate, ensuring that any potential issues with caching, volume mounts, or Dockerfile changes are addressed.

In summary, while docker-compose up --build -d --remove-orphans should rebuild your images and redeploy your application with the updated code, but there are scenarios where additional steps may be necessary to ensure that changes are properly applied. Using options like --no-cache and explicitly rebuilding images with docker-compose build, as well as removing containers and volumes with docker-compose down --remove-orphans, can help mitigate these issues.