docker go build docker-compose build-time

How to rebuild go project efficiently while using Docker Compose?

This may be a stupid question, but I'm new to using Docker-compose. So far, I love it... but I'm having some long build times. I have a project with several dependencies, and I need to obviously rebuild the source every time I make a change. Right now, I'm calling docker-compose build to rebuild the container, followed by a docker-compose up. The problem is:

It's rebuilding the entire container for every change I make to the source code (which takes a long time -- fetching dependencies/etc). This is significantly slowing me down.
I really feel like I should just be able to run a command on the container to rebuild and then re-run the executable, like-so:
```
docker-compose run web go build .
docker-compose run web ./app
```
or
```
docker-compose run web go build .
docker-compose restart
```
This should work because I'm using a volume to share code amongst the host and container. There shouldn't be a need to refetch all the dependencies. Shouldn't it use the freshly built executable? However, this does not reflect the built changes and port forwarding appears to break.

For reference, here is my Dockerfile:

FROM golang:1.8

COPY . /go/src/github.com/codeblooded/test1
WORKDIR /go/src/github.com/codeblooded/test1

RUN echo $PATH
RUN go get -d -v ./...
RUN go install -v ./...

RUN go build -o test1 .
CMD ["test1"]
EXPOSE 3470

And my docker-compose.yml file:

version: '3'
services:
  postgres:
    image: postgres
    volumes:
      - ./db/data/psql:/var/lib/postgresql/data
      - ./db/schema:/db/schema
  redis:
    image: redis
    volumes:
      - ./db/data/redis:/data
  server:
    build: .
    command: test1
    volumes:
      - .:/go/src/github.com/codeblooded/test1
    ports:
      - "3470:3470"
    depends_on:
      - postgres
      - redis

Is there something I'm missing?

Solution

You have asked a good question.

The command's order in the Dockerfile really matters. Put first the things that don't change frequently, and later those that are most likely to change in every build:

FROM golang:1.8

RUN go get -d -v ./...
RUN go install -v ./...

COPY . /go/src/github.com/codeblooded/test1
WORKDIR /go/src/github.com/codeblooded/test1

RUN echo $PATH

RUN go build -o test1 .
CMD ["test1"]
EXPOSE 3470

When a layer change regarding the previous build, docker discards the following cached layers and runs them again, sometimes wasting your time.

Pay attention to the "Using cache" sentence that docker outputs in each layer that is re-used from the previous build.

Another recommendation, for your dev work, use fresh to re-build your go app automatically every time you change the code. Just install it in the container and simply using command: fresh in your docker-compose.yml