Brian Rosmaita 1d672be72f Update Queens info about Glance and uWSGI

Adds a "Known Issues" releasenote and updates the "running glance
under httpd" documentation.

Change-Id: Ifc315b40cea23af95fc969a9c3a9479e8692792c
(cherry picked from commit 3d5f33f2b3)

2018-02-16 16:50:40 +00:00

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Running Glance in HTTPD

Since the Pike release Glance has packaged a wsgi script entrypoint that enables you to run it with a real web server like Apache HTTPD or nginx. To deploy this there are several patterns. This doc shows two common ways of deploying Glance with Apache HTTPD.

Warning

As pointed out in the Pike and Queens release notes (see the "Known Issues" section of each), the Glance project team recommends that Glance be run in its normal standalone configuration, particularly in production environments. The full functionality of Glance is not available when Glance is deployed in the manner described in this document. In particular, the interoperable image import functionality does not work under such configuration. See the release notes for details.

uWSGI Server HTTP Mode

This is the current recommended way to deploy Glance with Apache HTTP and it is how we deploy Glance for testing every proposed commit to OpenStack. In this deployment method we use the uWSGI server as a web server bound to a random local port. Then we configure apache using mod_proxy to forward all incoming requests on the specified endpoint to that local webserver. This has the advantage of letting apache manage all inbound http connections, but letting uWSGI manage running the python code. It also means when we make changes to Glance code or configuration we don't need to restart all of apache (which may be running other services too) and just need to restart the local uWSGI daemon.

The httpd/ directory contains sample files for configuring HTTPD to run Glance under the uWSGI server in this configuration. To use the sample configs simply copy httpd/uwsgi-glance-api.conf to the appropriate location for your Apache server. On Debian/Ubuntu systems it is:

/etc/apache2/sites-available/uwsgi-glance-api.conf

On Red Hat based systems it is:

/etc/httpd/conf.d/uwsgi-glance-api.conf

Enable mod_proxy by running sudo a2enmod proxy

Then on Ubuntu/Debian systems enable the site by creating a symlink from the file in sites-available to sites-enabled. (This is not required on Red Hat based systems):

ln -s /etc/apache2/sites-available/uwsgi-glance-api.conf /etc/apache2/sites-enabled

Start or restart HTTPD to pick up the new configuration.

Note

Be careful when setting up other proxies/endpoints in the same VirtualHost on Apache HTTPD using. If any are using SetEnv proxy-sendcl 1 then Apache HTTPD will buffer the incoming request to local disk before sending it to glance. This will likely cause problems when running in this configuration and is not necessary. (However, it is necessary if using mod_proxy_uwsgi.) For more details, see the section on mod_proxy_uwsgi below.

Now we need to configure and start the uWSGi service. Copy the httpd/glance-api-uwsgi.ini file to /etc/glance. Update the file to match your system configuration (for example, you'll want to set the number of processes and threads).

Install the uWSGI server and start the glance-api server using uWSGI:

sudo pip install uwsgi
uwsgi --ini /etc/glance/glance-api-uwsgi.ini

Note

In the sample configs port 60999 is used, but this doesn't matter and is just a randomly selected number. This is not a contract on the port used for the local uwsgi daemon.

mod_proxy_uwsgi

Warning

Running Glance under HTTPD in this configuration will only work on Python 2 if you use Transfer-Encoding: chunked. Also if running with Python 2 Apache will be buffering the chunked encoding before passing the request on to uWSGI. See bug: https://github.com/unbit/uwsgi/issues/1540

Instead of running uWSGI as a webserver listening on a local port and then having Apache HTTP proxy all the incoming requests with mod_proxy. The normally recommended way of deploying the uWSGI server with Apache HTTPD is to use mod_proxy_uwsgi and set up a local socket file for uWSGI to listen on. Apache will send the requests using the uwsgi protocol over this local socket file. However, there are issues with doing this and using chunked-encoding, so this is not recommended for use with Glance.

You can work around these issues by configuring your Apache proxy to buffer the chunked data and send the full content length to the uWSGI server. You do this by adding:

SetEnv proxy-sendcl 1

to the apache config file using mod_proxy_uwsgi. For more details on using mod_proxy_uwsgi see the official docs: http://uwsgi-docs.readthedocs.io/en/latest/Apache.html?highlight=mod_uwsgi_proxy#mod-proxy-uwsgi

There are some additional considerations when doing this though. Having Apache locally buffer the chunked data to disk before passing it to uWSGI means you'll need to have sufficient disk space in /tmp (or whatever you set TMPDIR to) to store all the disk files. The other aspect to consider is that this buffering can take some time to write the images to disk. To prevent random failures you'll likely have to increase timeout values in the uWSGI configuration file to ensure uWSGI will wait long enough for this to happen. (Depending on the uploaded image file sizes it may be necessary to set the timeouts to multiple minutes.)

mod_wsgi

This deployment method is not recommended for using Glance. The mod_wsgi protocol does not support Transfer-Encoding: chunked and therefore makes it unsuitable for use with Glance. However, you could theoretically deploy Glance using mod_wsgi but it will fail on any requests that use a chunked transfer encoding.

Glossary

uwsgi

The native protocol used by the uWSGI server. (The acronym is written in all lowercase on purpose.)

https://uwsgi-docs.readthedocs.io/en/latest/Protocol.html

uWSGI

A project that aims at developing a full stack for building hosting services. It produces software, the uWSGI server, that is exposed in Python code as a module named uwsgi.

https://uwsgi-docs.readthedocs.io/en/latest/index.html

https://pypi.python.org/pypi/uWSGI

https://github.com/unbit/uwsgi

mod_wsgi