How to rebuild dockerfile quick by using cache?

An update to previous answers, current docker build accepts --build-arg that pass environment variables like http_proxy without saving it in the resulting image.

Example:

# get squiddocker run --name squid -d --restart=always \  --publish 3128:3128 \  --volume /var/spool/squid3 \  sameersbn/squid:3.3.8-11# optionally in another terminal run tail on logsdocker exec -it squid tail -f /var/log/squid3/access.log# get squid ip to use in docker buildSQUID_IP=$(docker inspect --format '{{ .NetworkSettings.IPAddress }}' squid)# build your instancedocker build --build-arg http_proxy=http://$SQUID_IP:3128 .

Just use an intermediate/base image:

Base Dockerfile, build it with docker build -t custom-base or something:

FROM centos:6.4RUN yum update -yRUN yum install -y openssh-server vimRUN sed -i -e 's:keepcache=0:keepcache=1:' /etc/yum.conf

Application Dockerfile:

FROM custom-baseVOLUME ["/var/cache/yum/x86_64/6"] EXPOSE 22

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 <replicator-user> --dport 80 -j REDIRECT --to-port 8080

Disable redirect:

> iptables -t nat -D OUTPUT -p tcp -m owner ! --uid-owner <replicator-user> --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.