Why Google Cloud Build creates intermediate containers?

Question

Could somebody explain to me why Google Cloud Build creates intermediate containers to run commands?

Step #0 - "Build": Step 2/25 : ARG NODE_ENV
Step #0 - "Build":  ---> Running in 17281bea0e29
Step #0 - "Build": Removing intermediate container 17281bea0e29
Step #0 - "Build":  ---> a43229632036
Step #0 - "Build": Step 3/25 : ARG DB_NAME
Step #0 - "Build":  ---> Running in 04a199971761
Step #0 - "Build": Removing intermediate container 04a199971761
Step #0 - "Build":  ---> 3f15b2ad5662
Step #0 - "Build": Step 4/25 : ARG DB_USER
Step #0 - "Build":  ---> Running in 4fb95096aab1
Step #0 - "Build": Removing intermediate container 4fb95096aab1
Step #0 - "Build":  ---> 97c619b21472
Step #0 - "Build": Step 5/25 : ARG DB_PASSWORD
Step #0 - "Build":  ---> Running in 2280e3095a20
Step #0 - "Build": Removing intermediate container 2280e3095a20
Step #0 - "Build":  ---> a79acad9a411
Step #0 - "Build": Step 6/25 : ARG CLOUD_SQL_CONNECTION_NAME
Step #0 - "Build":  ---> Running in 1f63bde588f0
Step #0 - "Build": Removing intermediate container 1f63bde588f0
Step #0 - "Build":  ---> 8e22be5c6191
Step #0 - "Build": Step 7/25 : ENV NODE_ENV ${NODE_ENV}
Step #0 - "Build":  ---> Running in 6f5495791d72
Step #0 - "Build": Removing intermediate container 6f5495791d72
Step #0 - "Build":  ---> 2413826fa5f6
Step #0 - "Build": Step 8/25 : ENV DB_NAME ${DB_NAME}
Step #0 - "Build":  ---> Running in e3099226a900
Step #0 - "Build": Removing intermediate container e3099226a900
Step #0 - "Build":  ---> 68f11d7cee19
Step #0 - "Build": Step 9/25 : ENV DB_USER ${DB_USER}
Step #0 - "Build":  ---> Running in c1c3dc6ca115
Step #0 - "Build": Removing intermediate container c1c3dc6ca115
Step #0 - "Build":  ---> 5fd5610b2de5
Step #0 - "Build": Step 10/25 : ENV DB_PASSWORD ${DB_PASSWORD}
Step #0 - "Build":  ---> Running in 67c6ed7a56e7
Step #0 - "Build": Removing intermediate container 67c6ed7a56e7
Step #0 - "Build":  ---> 7c8ecb080c59
Step #0 - "Build": Step 11/25 : ENV CLOUD_SQL_CONNECTION_NAME ${CLOUD_SQL_CONNECTION_NAME}
Step #0 - "Build":  ---> Running in 8dddcddd80c0
Step #0 - "Build": Removing intermediate container 8dddcddd80c0
Step #0 - "Build":  ---> 789cc6e25b55
Step #0 - "Build": Step 12/25 : WORKDIR /usr/src/app
Step #0 - "Build":  ---> Running in 2c5e9083a8a5
Step #0 - "Build": Removing intermediate container 2c5e9083a8a5

I am interested in Removing intermediate container ... after each step. Does it hurt the performance of the build?

cloudbuild.yml

steps:
  - name: gcr.io/cloud-builders/docker
    args:
      - build
      - '--build-arg'
      - NODE_ENV=$_NODE_ENV
      - '--build-arg'
      - DB_NAME=$_DB_NAME
      - '--build-arg'
      - DB_USER=$_DB_USER
      - '--build-arg'
      - DB_PASSWORD=$$DB_PASSWORD
      - '--build-arg'
      - CLOUD_SQL_CONNECTION_NAME=$_CLOUD_SQL_CONNECTION_NAME
      - '--no-cache'
      - '-t'
      - '$_GCR_HOSTNAME/$PROJECT_ID/$REPO_NAME/$_SERVICE_NAME:$COMMIT_SHA'
      - .
      - '-f'
      - Dockerfile
    id: Build
    secretEnv:
      - DB_PASSWORD
  - name: gcr.io/cloud-builders/docker
...

score 3 · Accepted Answer · answered Jun 10 '21 at 01:54

Cloud Build uses Docker to execute builds. To understand why Cloud Build creates intermediate containers, first you must understand the Docker build process.

For each build step, Cloud Build executes a Docker container as an instance of docker run. Each step is processed in an intermediate container.

"Those intermediate containers can succeed or fail. If they succeed, the intermediate container is merged with the image from the last successful build step, and then the intermediate container is deleted."

On the performance perspective, removing immediate containers are part of the build process and it helps reduce the size of your container image.

There are already some existing articles that further explains the Docker build process. Here are some interesting links:

Why Google Cloud Build creates intermediate containers?

1 Answers1