I was in trouble because the behavior of docker container did not change

Introduction

Even if I changed the code, the behavior of the application in the container did not change, which was a problem. This is a memo about how to deal with it. (It is not the system that the cache worked)

Remedy first

The ʻapp (executable file) built in the Dockerfile was overwritten by the ʻapp in the local directory of volumes set in docker-compose.yml. Therefore, I solved it by changing it so that it would not be mounted excessively.

Problem

1. I have a golang app that I was creating in a docker container
2. I try to buy and start the app in Dockerfile
3. For example, edit and save main.go.
4. Recreate and launch the app with docker-compose up -d --build
5. That? It hasn't changed! ?? (Build is running)
6. Try docker-compose build --no-cache but the same ...

Directory structure ↓

myapp
 - docker-compose.yml
 - Go
    - Dockerfile
    - main.go
    - app

Partial code excerpt ↓

Dockerfile

FROM golang:1.12.12-alpine3.9 AS build

ENV GOPATH $GOPATH:/go
ENV PATH $PATH:$GOPATH/bin
ENV GO111MODULE=on

hogehoge

COPY . /go/src/app
WORKDIR /go/src/app
RUN go build -o app main.go
CMD ["./app"]

docker-compose.yml

version: '2'
services:
  app:
    build:
      context: ./Go
      dockerfile: Dockerfile
    volumes:
      - "./Go:/go/src/app"
    container_name: go_app
    ports:
      - "127.0.0.1:8080:8080"
    tty: true
    restart: always

Cause

The cause was the local app I was trying to create. The command execution order is RUN → volumes → CMD, and the ʻapp built in the container was overwritten with the local ʻapp.

approach

Don't mount extra files

In this case, only the session information had to be persisted and saved, so this one file was sufficient for sharing the file.

docker-compose.yml

    volumes:
      - "./Go/sessions:/go/src/app/sessions"

Exclude files that should not be shared

During development, it is more convenient to mount and edit the source code. Therefore, I thought it would be a good idea not to share only ʻapp`. (How to exclude some when mounting Volume with Docker)

in conclusion

In the first place, while I was making code changes for the purpose of persisting session information, something like this. (There is also a difference between the production server and the development server) Eventually, we will move to database management. (Of which)