Just putting the finishing touches on a new Ansible Tower Workshop, testing an additional exercise, building my Docker container locally before I push the changes to the repo to build my production image in Docker Hub.
So as I'm sitting here in the Nashville Airport waiting for this container to build and a bit of time to pass for us to board, I figured it'd be a good time to do a bit of writing. Here's a trick I use that can save you hours in building containers...
The Premise
I start with a very basic Alpine image and add my needed packages - a few from the apk package manager, but then I compile nginx from source. This is because it's much easier to set proper operating conditions for the nginx server in a container. Then, after the nginx server is compiled and ready to roll, I build my application and dump it into /var/www/html
The Problem
Now, compiling nginx from source takes time. I have separate RUN stanzas in the Dockerfile to benefit from the image layering that container images provide, but Docker isn't always that great at detecting changes. If I make a few changes to the web application, Docker doesn't always copy over the new files.
To quickly fix this, one could prune the built images in the local cache - but this means starting from the top, which means recompiling nginx, which takes a good deal of time.
The Solution
How do we tell Docker explicitly where to start from? Just add an ENV between your static and dynamic actions, then change a small variable in between builds.
FROM node:8-alpine # Install base packages RUN apk -U add wget tar gzip git asciidoctor # Install nginx RUN \ build_pkgs="build-base linux-headers openssl-dev pcre-dev wget zlib-dev" && \ runtime_pkgs="ca-certificates openssl pcre zlib" && \ apk --update add ${build_pkgs} ${runtime_pkgs} && \ cd /tmp && \ wget http://nginx.org/download/nginx-1.15.8.tar.gz && \ tar xzf nginx-1.15.8.tar.gz && \ cd /tmp/nginx-1.15.8 && \ ./configure \ --prefix=/etc/nginx \ --sbin-path=/usr/sbin/nginx \ --conf-path=/etc/nginx/nginx.conf \ --error-log-path=/var/log/nginx/error.log \ --http-log-path=/var/log/nginx/access.log \ --pid-path=/tmp/run/nginx.pid \ --lock-path=/tmp/run/nginx.lock \ --http-client-body-temp-path=/tmp/cache/nginx/client_temp \ --http-proxy-temp-path=/tmp/cache/nginx/proxy_temp \ --http-fastcgi-temp-path=/tmp/cache/nginx/fastcgi_temp \ --http-uwsgi-temp-path=/tmp/cache/nginx/uwsgi_temp \ --http-scgi-temp-path=/tmp/cache/nginx/scgi_temp \ --user=nginx \ --group=nginx \ --with-http_ssl_module \ --with-http_realip_module \ --with-http_addition_module \ --with-http_sub_module \ --with-http_dav_module \ --with-http_flv_module \ --with-http_mp4_module \ --with-http_gunzip_module \ --with-http_gzip_static_module \ --with-http_random_index_module \ --with-http_secure_link_module \ --with-http_stub_status_module \ --with-http_auth_request_module \ --with-mail \ --with-mail_ssl_module \ --with-file-aio \ --with-ipv6 \ --with-threads \ --with-stream \ --with-stream_ssl_module \ --with-http_slice_module \ --with-http_v2_module && \ make && \ make install && \ ln -sf /dev/stdout /var/log/nginx/access.log && ln -sf /dev/stderr /var/log/nginx/error.log && \ adduser -D nginx && \ rm -rf /tmp/* && \ apk del ${build_pkgs} && \ rm -rf /var/cache/apk/* && \ mkdir -p /tmp/cache/nginx/scgi_temp && \ mkdir -p /tmp/cache/nginx/uwsgi_temp && \ mkdir -p /tmp/cache/nginx/fastcgi_temp && \ mkdir -p /tmp/cache/nginx/proxy_temp && \ mkdir -p /tmp/cache/nginx/client_temp && \ mkdir -p /tmp/run ENV cacheBUSTER v9001 COPY conf/nginx.conf /etc/nginx/nginx.conf COPY webapp/* /var/www/html/ Now, simply change that cacheBuster ENV definition to some other string and enjoy a cached image layer with nginx while being able to pull in fresh application data every time!
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