How to make Docker Compose builds faster?

Question

While building new Docker images within Docker Machine environment I noticed that docker-compose build app command freezes for 10-12 minutes before it starts actual build process:

$ docker-compose build app
Building app

... 10 minutes ...

Step 1/10 : FROM ruby:2.4.1
 ---> e7ca4a0b5b6d
...

I tried to use --verbose parameter to make it more descriptive, but that didn't actually help:

$ docker-compose --verbose build
compose.config.config.find: Using configuration files: ./docker-compose.yml
docker.auth.find_config_file: Trying paths: ['/Users/vtambourine/.docker/config.json', '/Users/vtambourine/.dockercfg']
docker.auth.find_config_file: Found file at path: /Users/vtambourine/.docker/config.json
docker.auth.load_config: Couldn't find 'auths' or 'HttpHeaders' sections
docker.auth.parse_auth: Auth data for {0} is absent. Client might be using a credentials store instead.
compose.cli.command.get_client: docker-compose version 1.14.0, build c7bdf9e
docker-py version: 2.3.0
CPython version: 2.7.12
OpenSSL version: OpenSSL 1.0.2j  26 Sep 2016
compose.cli.command.get_client: Docker base_url: https://146.185.007.007:2376
compose.cli.command.get_client: Docker version: KernelVersion=4.9.0-3-amd64, Arch=amd64, BuildTime=2017-09-05T19:58:57.182575033+00:00, ApiVersion=1.30, Version=17.06.2-ce, MinAPIVersion=1.12, GitCommit=cec0b72, Os=linux, GoVersion=go1.8.3
compose.project.build: db uses an image, skipping
compose.service.build: Building app
compose.cli.verbose_proxy.proxy_callable: docker build <- (pull=False, cache_from=None, stream=True, nocache=False, labels=None, tag='aerostat:app', buildargs={}, forcerm=False, rm=True, path='/Users/vtambourine/Code/aerostat', dockerfile='containers/development/Dockerfile')
docker.api.build._set_auth_headers: Looking for auth config
docker.api.build._set_auth_headers: Sending auth config (u'auths')
compose.cli.verbose_proxy.proxy_callable: docker build -> <generator object _stream_helper at 0x10b61f230>

... 10 minutes ...

Step 1/10 : FROM ruby:2.4.1
---> e7ca4a0b5b6d

Is there any way to understand, what is going and how to make build process faster?

Answer 1

Big thanks to Tarun Lalwani I learned about Docker context.

The build context is a set of files located at a specified location. Is my (the most trivial) case location is simply . — project directory. The first thing a build process does is copy entire context to the daemon. Since I'm using Docker Machine to deploy my containers Docker daemon sits on the remote host, which cause the entire project folder being send to the server via internet.

With all unnecessary for production folders, such as .git, tmp, total size was way almost 200 MB:

$ docker build -t my-app -f containers/production/Dockerfile .
Sending build context to Docker daemon  187.9MB

By using simple .dockerignore rules I was able to reduce it dramatically:

$ docker build -t my-app -f containers/production/Dockerfile .
Sending build context to Docker daemon  151kB

Lesson learned — use .dockerignore.

Detailed explanation can be found at Dockerfile reference.