Content Cache

Content Cache Operator

A Juju charm for deploying and managing a content cache.

Overview

A service for caching content, built on top of Nginx configurable to cache any http or https web site. Tuning options include cache storage size, maximum request size to cache and cache validity duration.

This service was developed to provide front-end caching for web sites run by Canonical's IS team, and to reduce the need for third-party CDNs by providing high-bandwidth access to web sites via this caching front-end. Currently used for a number of services including the Snap Store, the majority of Canonical's web properties including ubuntu.com and canonical.com, and Ubuntu Extended Security Maintenance.

This Kubernetes-based version is built using the same approach, and can be used as a front-end caching service in a situation where your Kubernetes cluster and its ingress controllers have a fast connection to the Internet.

Usage

For details on using Kubernetes with Juju see here, and for details on using Juju with MicroK8s for easy local testing see here.

To deploy this charm into a k8s model, with sample configuration set up to cache archive.ubuntu.com on archive.local:

juju deploy cs:~content-cache-charmers/content-cache-k8s \
    --config site=archive.local \
    --config backend=http://archive.ubuntu.com:80 \
    --config juju-external-hostname=archive.local
juju expose content-cache

And then you can test the deployment with:

# Set this to to the "Address" value in the "App" section of `juju status`
APP_IP=10.152.183.117

First let's request a resource with headers that will allow us to cache (with sample output):

curl -v --resolve archive.local:80:${APP_IP} http://archive.local/ubuntu/dists/focal/Contents-i386.gz -o /dev/null 2>&1 | grep 'X-Cache-Status'
# < X-Cache-Status: MISS from juju-87625f-hloeung-13 (content-cache-56bbcd79d6-h8dk2)
#  First result is a cache MISS
curl -v --resolve archive.local:80:${APP_IP} http://archive.local/ubuntu/dists/focal/Contents-i386.gz -o /dev/null 2>&1 | grep 'X-Cache-Status'
# < X-Cache-Status: HIT from juju-87625f-hloeung-13 (content-cache-56bbcd79d6-h8dk2)
#  Second result is a cache HIT

And now let's request a resource which has headers telling us not to cache:

# Verify cache control headers on the upstream resource
curl -v http://archive.ubuntu.com/ubuntu/dists/focal/Release 2>&1 | grep 'Cache-Control'
#   output: < Cache-Control: max-age=0, proxy-revalidate
# And now perform the requests through the content-caching service
curl -v --resolve archive.local:80:${APP_IP} http://archive.local/ubuntu/dists/focal/Release -o /dev/null 2>&1 | grep 'X-Cache-Status'
# < X-Cache-Status: MISS from juju-87625f-hloeung-13 (content-cache-56bbcd79d6-h8dk2)
#  First result is a cache MISS
curl -v --resolve archive.local:80:${APP_IP} http://archive.local/ubuntu/dists/focal/Release -o /dev/null 2>&1 | grep 'X-Cache-Status'
# < X-Cache-Status: MISS from juju-87625f-hloeung-13 (content-cache-56bbcd79d6-h8dk2)
#  Second result still a cache MISS

For more details, see here