docker: add Docker files for running an Apache mod_wsgi server

docker: add Docker files for running an Apache mod_wsgi server

I frequently find myself wanting to run hgweb in a production-like
environment, with a real HTTP server and multiple WSGI workers.

This patch introduces a Docker environment for running Mercurial
under Apache + mod_wsgi. With just a few command executions, it is
possible to spin up a Docker container running hgweb.

The container is tailored for Mercurial developers wanting to run
Mercurial from a source checkout. It is **not** meant to be something
suitable for production use.

The container provides a default hgweb environment with an empty
repository that allows pushes. You can thus start a container and push
your favorite repository there for quick testing.

The container is designed to allow customizations. Users can provide
their own hgweb configurations and mount existing directories containing
repositories into the container.

The behavior of the container and how to control things is documented in
the README.rst file.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/apache-server/Dockerfile	Tue Nov 11 20:32:10 2014 -0800
@@ -0,0 +1,23 @@
+FROM debian:wheezy
+
+ENV DEBIAN_FRONTEND noninteractive
+ENV WSGI_PROCESSES 4
+ENV WSGI_THREADS 1
+ENV WSGI_MAX_REQUESTS 100000
+
+EXPOSE 80
+VOLUME ["/var/hg/htdocs", "/var/hg/repos"]
+
+RUN apt-get update && apt-get -y install libapache2-mod-wsgi python-dev vim
+
+# Install our own Apache site.
+RUN a2dissite 000-default
+ADD vhost.conf /etc/apache2/sites-available/hg
+RUN a2ensite hg
+
+ADD hgwebconfig /defaulthgwebconfig
+
+ADD entrypoint.sh /entrypoint.sh
+ENTRYPOINT ["/entrypoint.sh"]
+
+CMD ["/usr/sbin/apache2", "-DFOREGROUND"]

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/apache-server/README.rst	Tue Nov 11 20:32:10 2014 -0800
@@ -0,0 +1,144 @@
+====================
+Apache Docker Server
+====================
+
+This directory contains code for running a Mercurial hgweb server via
+mod_wsgi with the Apache HTTP Server inside a Docker container.
+
+.. important::
+
+   This container is intended for testing purposes only: it is
+   **not** meant to be suitable for production use.
+
+Building Image
+==============
+
+The first step is to build a Docker image containing Apache and mod_wsgi::
+
+  $ docker build -t hg-apache .
+
+.. important::
+
+   You should rebuild the image whenever the content of this directory
+   changes. Rebuilding after pulling or when you haven't run the container
+   in a while is typically a good idea.
+
+Running the Server
+==================
+
+To run the container, you'll execute something like::
+
+  $ docker run --rm -it -v `pwd`/../../..:/var/hg/source -p 8000:80 hg-apache
+
+If you aren't a Docker expert:
+
+* ``--rm`` will remove the container when it stops (so it doesn't clutter
+  your system)
+* ``-i`` will launch the container in interactive mode so stdin is attached
+* ``-t`` will allocate a pseudo TTY
+* ``-v src:dst`` will mount the host filesystem at ``src`` into ``dst``
+  in the container. In our example, we assume you are running from this
+  directory and use the source code a few directories up.
+* ``-p 8000:80`` will publish port ``80`` on the container to port ``8000``
+  on the host, allowing you to access the HTTP server on the host interface.
+* ``hg-apache`` is the container image to run. This should correspond to what
+  we build with ``docker build``.
+
+.. important::
+
+   The container **requires** that ``/var/hg/source`` contain the Mercurial
+   source code.
+
+   Upon start, the container will attempt an install of the source in that
+   directory. If the architecture of the host machine doesn't match that of
+   the Docker host (e.g. when running Boot2Docker under OS X), Mercurial's
+   Python C extensions will fail to run. Be sure to ``make clean`` your
+   host's source tree before mounting it in the container to avoid this.
+
+When starting the container, you should see some start-up actions (including
+a Mercurial install) and some output saying Apache has started::
+
+Now if you load ``http://localhost:8000/`` (or whatever interface Docker
+is using), you should see hgweb running!
+
+For your convenience, we've created an empty repository available at
+``/repo``. Feel free to populate it with ``hg push``.
+
+Customizing the Server
+======================
+
+By default, the Docker container installs a basic hgweb config and an
+empty dummy repository. It also uses some reasonable defaults for
+mod_wsgi.
+
+Customizing the WSGI Dispatcher And Mercurial Config
+----------------------------------------------------
+
+By default, the Docker environment installs a custom ``hgweb.wsgi``
+file (based on the example in ``contrib/hgweb.wsgi``). The file
+is installed into ``/var/hg/htdocs/hgweb.wsgi``.
+
+A default hgweb configuration file is also installed. The ``hgwebconfig``
+file from this directory is installed into ``/var/hg/htdocs/config``.
+
+You have a few options for customizing these files.
+
+The simplest is to hack up ``hgwebconfig`` and ``entrypoint.sh`` in
+this directory and to rebuild the Docker image. This has the downside
+that the Mercurial working copy is modified and you may accidentally
+commit unwanted changes.
+
+The next simplest is to copy this directory somewhere, make your changes,
+then rebuild the image. No working copy changes involved.
+
+The preferred solution is to mount a host file into the container and
+overwrite the built-in defaults.
+
+For example, say we create a custom hgweb config file in ``~/hgweb``. We
+can start the container like so to install our custom config file::
+
+  $ docker run -v ~/hgweb:/var/hg/htdocs/config ...
+
+You can do something similar to install a custom WSGI dispatcher::
+
+  $ docker run -v ~/hgweb.wsgi:/var/hg/htdocs/hgweb.wsgi ...
+
+Managing Repositories
+---------------------
+
+Repositories are served from ``/var/hg/repos`` by default. This directory
+is configured as a Docker volume. This means you can mount an existing
+data volume container in the container so repository data is persisted
+across container invocations. See
+https://docs.docker.com/userguide/dockervolumes/ for more.
+
+Alternatively, if you just want to perform lightweight repository
+manipulation, open a shell in the container::
+
+  $ docker exec -it <container> /bin/bash
+
+Then run ``hg init``, etc to manipulate the repositories in ``/var/hg/repos``.
+
+mod_wsgi Configuration Settings
+-------------------------------
+
+mod_wsgi settings can be controlled with the following environment
+variables.
+
+WSGI_PROCESSES
+   Number of WSGI processes to run.
+WSGI_THREADS
+   Number of threads to run in each WSGI process
+WSGI_MAX_REQUESTS
+   Maximum number of requests each WSGI process may serve before it is
+   reaped.
+
+See https://code.google.com/p/modwsgi/wiki/ConfigurationDirectives#WSGIDaemonProcess
+for more on these settings.
+
+.. note::
+
+   The default is to use 1 thread per process. The reason is that Mercurial
+   doesn't perform well in multi-threaded mode due to the GIL. Most people
+   run a single thread per process in production for this reason, so that's
+   what we default to.

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/apache-server/entrypoint.sh	Tue Nov 11 20:32:10 2014 -0800
@@ -0,0 +1,80 @@
+#!/bin/bash
+
+# This script gets executed on container start. Its job is to set up
+# the Mercurial environment and invoke the server.
+
+# Mercurial can be started in two modes.
+# If the MERCURIAL_SOURCE environment variable is set and it points to a
+# Mercurial source directory, we will install Mercurial from that directory.
+# Otherwise, we download the Mercurial source and install it manually.
+
+set -e
+
+SOURCE_DIR=/var/hg/source
+INSTALL_DIR=/var/hg/install
+REPOS_DIR=/var/hg/repos
+HTDOCS_DIR=/var/hg/htdocs
+
+if [ ! -d ${SOURCE_DIR} ]; then
+  echo "Mercurial source not available at ${SOURCE_DIR}"
+  echo "You need to mount a volume containing the Mercurial source code"
+  echo "when running the container. For example:"
+  echo ""
+  echo "  $ docker run -v ~/src/hg:/${SOURCE_DIR} hg-apache"
+  echo ""
+  echo "This container will now stop running."
+  exit 1
+fi
+
+echo "Installing Mercurial from ${SOURCE_DIR} into ${INSTALL_DIR}"
+pushd ${SOURCE_DIR}
+/usr/bin/python2.7 setup.py install --root=/ --prefix=${INSTALL_DIR} --force
+popd
+
+mkdir -p ${HTDOCS_DIR}
+
+# Provide a default config if the user hasn't supplied one.
+if [ ! -f ${HTDOCS_DIR}/config ]; then
+  cp /defaulthgwebconfig ${HTDOCS_DIR}/config
+fi
+
+if [ ! -f ${HTDOCS_DIR}/hgweb.wsgi ]; then
+  cat >> ${HTDOCS_DIR}/hgweb.wsgi << EOF
+config = '${HTDOCS_DIR}/config'
+
+import sys
+sys.path.insert(0, '${INSTALL_DIR}/lib/python2.7/site-packages')
+
+from mercurial import demandimport
+demandimport.enable()
+
+from mercurial.hgweb import hgweb
+application = hgweb(config)
+EOF
+fi
+
+mkdir -p ${REPOS_DIR}
+
+if [ ! -d ${REPOS_DIR}/repo ]; then
+  ${INSTALL_DIR}/bin/hg init ${REPOS_DIR}/repo
+  chown -R www-data:www-data ${REPOS_DIR}/repo
+fi
+
+# This is necessary to make debuginstall happy.
+if [ ! -f ~/.hgrc ]; then
+  cat >> ~/.hgrc << EOF
+[ui]
+username = Dummy User <[e-mail]>
+EOF
+fi
+
+echo "Verifying Mercurial installation looks happy"
+${INSTALL_DIR}/bin/hg debuginstall
+
+. /etc/apache2/envvars
+
+echo "Starting Apache HTTP Server on port 80"
+echo "We hope you remembered to publish this port when running the container!"
+echo "If this is an interactive container, simply CTRL^C to stop."
+
+exec "$@"

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/apache-server/hgwebconfig	Tue Nov 11 20:32:10 2014 -0800
@@ -0,0 +1,6 @@
+[paths]
+/ = /var/hg/repos/*
+
+[web]
+allow_push = *
+push_ssl = False

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/contrib/docker/apache-server/vhost.conf	Tue Nov 11 20:32:10 2014 -0800
@@ -0,0 +1,24 @@
+# Apache won't be able to resolve its own hostname, so we sneak this
+# into the global context to silence a confusing-to-user warning on
+# server start.
+ServerName hg
+
+<VirtualHost *:80>
+  DocumentRoot /var/hg/htdocs
+  <Directory />
+    Options FollowSymLinks
+    AllowOverride None
+  </Directory>
+
+  SetEnv HGENCODING UTF-8
+  SetEnv LC_TYPE UTF-8
+
+  WSGIDaemonProcess hg processes=${WSGI_PROCESSES} threads=${WSGI_THREADS} maximum-requests=${WSGI_MAX_REQUESTS} user=www-data group=www-data display-name=hg-wsgi
+  WSGIProcessGroup hg
+
+  WSGIScriptAliasMatch ^(.*) /var/hg/htdocs/hgweb.wsgi$1
+
+  ErrorLog ${APACHE_LOG_DIR}/error.log
+  LogLevel warn
+  CustomLog ${APACHE_LOG_DIR}/access.log combined
+</VirtualHost>