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The base image from Red Hat is quite small, on the order of 196M for RHEL 7.4. However it tends to be missing a lot of the bits and pieces that are required by the products I want to build new images for.

The moment I do a "yum install Xxx" on top of it the image size blows out to by +500M-800M.

Is there a way to reduce the size of the image?

TJA
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2 Answers2

57

Yes Docker image sizes can be dramatically reduced by doing a "yum clean all"

Initial RHEL Image Size = 196M

Dockerfile - RHEL Image(+bc) = 505M

# Build command
# docker build -t rhel7base:latest --build-arg REG_USER='<redhat_developer_user>' --build-arg REG_PSWD='<password>' --squash .

FROM registry.access.redhat.com/rhel7/rhel:latest

LABEL maintainer="tim"

ARG REG_USER=none
ARG REG_PSWD=none

RUN subscription-manager register --username $REG_USER --password $REG_PSWD --auto-attach && \
    subscription-manager repos --enable rhel-server-rhscl-7-rpms && \
    yum install -y bc

Dockerfile - RHEL Image(+bc) with "yum clean all" = 207M saving 298M

# Build command
# docker build -t rhel7base:latest --build-arg REG_USER='<redhat_developer_user>' --build-arg REG_PSWD='<password>' --squash .

FROM registry.access.redhat.com/rhel7/rhel:latest

LABEL maintainer="tim"

ARG REG_USER=none
ARG REG_PSWD=none

RUN subscription-manager register --username $REG_USER --password $REG_PSWD --auto-attach && \
    subscription-manager repos --enable rhel-server-rhscl-7-rpms && \
    yum install -y bc && \
    yum clean all && \
    rm -rf /var/cache/yum

NOTE: The --squash option comes as an experimental flag in the latest version of Docker. It compresses the layered file system into a single new layer https://blog.docker.com/2017/01/whats-new-in-docker-1-13/

I found the solution of using "yum clean all" at https://medium.com/@vaceletm/docker-layers-cost-b28cb13cb627

The addition of "rm -rf /var/cache/yum" comes from the suggestion in the output of the "yum clean all"

TJA
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5

Apart from TJA's answer, you can also use a smaller CentOS base image, for example, a Debian light exists, it is called Bitnami

https://hub.docker.com/r/bitnami/minideb-extras/

For CentOS maybe you can use

https://hub.docker.com/r/blalor/centos/

You can also try to reduce the size of your images using 2 tools

https://github.com/mvanholsteijn/strip-docker-image

and

https://github.com/docker-slim/docker-slim

user2915097
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  • Absolutely true, or even opt for something like Alpine. At the end of the day I suspect that yum clean all applies to those also. – TJA Sep 07 '17 at 08:49