How to rebuild dockerfile quick by using cache?

Question

I want to optimize my Dockerfile. And I wish to keep cache file in disk. But, I found when I run docker build . It always try to get every file from network.

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Answer 1

You should use a caching proxy (f.e Http Replicator, squid-deb-proxy ...) or apt-cacher-ng for Ubuntu to cache installation packages. I think, you can install this software to the host machine.

EDIT:

Option 1 - caching http proxy - easier method with modified Dockerfile:

> cd ~/your-project
> git clone https://github.com/gertjanvanzwieten/replicator.git
> mkdir cache
> replicator/http-replicator -r ./cache -p 8080 --daemon ./cache/replicator.log  --static   

add to your Dockerfile (before first RUN line):

ENV http_proxy http://172.17.42.1:8080/

You should optionally clear the cache from time to time.

Option 2 - caching transparent proxy, no modification to Dockerfile:

> cd ~/your-project
> curl -o r.zip https://codeload.github.com/zahradil/replicator/zip/transparent-requests
> unzip r.zip
> rm r.zip
> mv replicator-transparent-requests replicator
> mkdir cache
> replicator/http-replicator -r ./cache -p 8080 --daemon ./cache/replicator.log --static

You need to start the replicator as some user (non root!).

Set up the transparent redirect:

> iptables -t nat -A OUTPUT -p tcp -m owner ! --uid-owner  --dport 80 -j REDIRECT --to-port 8080

Disable redirect:

> iptables -t nat -D OUTPUT -p tcp -m owner ! --uid-owner  --dport 80 -j REDIRECT --to-port 8080

This method is the most transparent and general and your Dockerfile does not need to be modified. You should optionally clear the cache from time to time.