Advantages and Uses of Locally Cached Packages

Air-gapped Networks

Package mirroring is handy when switches do not have a direct connection to the Internet to receive updates or install software. Instead of reaching out to the Cumulus Networks repository on the Internet, switches configured to use a local mirror can reach out to a locally trusted target that has been configured.

Granular Control of Software Versions

Package mirroring is also a way to lock down switches from updating packages, as they cannot receive newer package versions from those that exist on the mirror, so by controlling what is on the mirror you can control what packages switches can install.

Standard package workflow: Packages downloaded directly from the Cumulus Networks repository by each switch.

Speed, Efficiency and Bandwidth Reduction

Switches that are configured to receive their packages from a local mirror get those packages from a local source, which generally means faster download times. The other benefit is package caching; if one switch downloads a package, the mirror caches that package so that all subsequent downloads occur directly from the mirror for added speed. Reducing external bandwidth requirements may be a concern depending on your scale and package needs.

Tools for Mirroring Packages

In traditional Linux form, there are a number of package mirroring tools available for Debian.

The apt-mirror program can copy the entire Cumulus Networks repository, so you can point your local switches at the local copy of the repository. This approach works, but is a bit more heavyweight than you may want. For that reason, we recommend using the apt-cacher-ng program.

apt-cacher-ng has been around for quite some time now and has many proponents. It replaces the original apt-cacher program as it is more robust.

apt-cacher-ng offers several benefits over other offerings:

• Small footprint: apt-cacher-ng uses fraction of the space of a full mirror, and the cache automatically clears old packages that are no longer requested.
• Reduced WAN bandwidth consumption: apt-cacher-ng downloads each package only once and caches it for subsequent requests from other switches.
• Faster package downloads: apt-cacher-ng reduces download time for all but the first request from a switch.
• Easy client configuration: Change a single file. Instead of changing repository URLs to point to new repositories, you simply add a new proxy to the configuration.
• Easy installation: Single package install, with no additional configuration in most cases. Simply install and go! There is no need to install an additional web server.

Installing and Configuring apt-cacher

Installing apt-cacher-ng on a Debian/Ubuntu Server

Before you install apt-cacher-ng, you need to reference the Debian Jessie upstream repository. Create a file called debian.list in the /etc/apt/sources.list.d/ directory and add the following lines:

deb  http://deb.debian.org/debian jessie main
deb-src  http://deb.debian.org/debian jessie main

After you save the file, apt-cacher-ng should be available:

cumulus@cumulus:mgmt-vrf:~$ sudo apt-cache policy apt-cacher-ng
apt-cacher-ng:
  Installed: (none)
  Candidate: 0.8.0-3
  Version table:
     0.8.0-3 0
        500 http://deb.debian.org/debian/ jessie/main amd64 Packages

Now you are ready to install the apt-cacher-ng package:

$ sudo apt-get update -y
$ sudo apt-get install apt-cacher-ng

Configuring Switches to Use the Apt-Cacher as a Proxy

Create the file /etc/apt/apt.conf.d/90apt-proxy and add the following line in the file:

Acquire::http::Proxy "http://192.168.252.254:3142";

Note: Remember to update the IP address to reflect the IP address of your server running apt-cacher-ng.

Other Helpful Tips

Don't Mix Packages from Different Distributions

Cumulus Networks strongly recommends you do not install packages from one Linux distribution onto another distribution. For example, do not install any Ubuntu packages on a Cumulus Linux switch, since Cumulus Linux is based on Debian.

Freezing Package State

To freeze your package state, simply turn off the apt-cacher-ng daemon on the server. All of the switches become frozen at their software revisions until the daemon is started again.

If you are using systemd on your mirror server, run:

$ sudo systemctl stop apt-cacher-ng

If you are not using systemd, run this command instead:

$ sudo service apt-cacher-ng stop

Clearing Package Cache on Upgrades

It may make sense to clear the package cache after certain events, such as upgrading to a new version of Cumulus Linux or for whenever you want to serve a new version of an existing package.

To clear the package cache for a Cumulus Linux 3.x repository on Ubuntu 16.04, run the following command:

$ sudo rm -rfv /var/cache/apt-cacher-ng/repo3.cumulusnetworks.com/repo/dists/