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Running Frontier Squid in a Container

Frontier Squid is a distribution of the well-known squid HTTP caching proxy software that is optimized for use with applications on the Worldwide LHC Computing Grid (WLCG). It has many advantages over regular squid for common grid applications, especially Frontier and CVMFS. The OSG distribution of frontier-squid is a straight rebuild of the upstream frontier-squid package for the convenience of OSG users.


OSG recommends that all sites run a caching proxy for HTTP to help reduce bandwidth and improve throughput.

This document outlines how to run Frontier Squid in a Docker container.

Before Starting

Before starting the installation process, consider the following points (consulting the Frontier Squid Reference section as needed):

  1. Docker: For the purpose of this guide, the host must have a running docker service and you must have the ability to start containers (i.e., belong to the docker Unix group).
  2. Network ports: Frontier squid communicates on ports 3128 (TCP) and 3401 (UDP).
    • We encourage sites to allow monitoring on port 3401 via UDP from CERN IP address ranges,,, and See the CERN monitoring documentation for additional details.
    • If outgoing connections are filtered, note that CVMFS always uses ports 8000, 80, or 8080.
  3. Host choice: If you will be supporting the Frontier application at your site, review the upstream documentation to determine how to size your equipment.

Configuring Squid

Environment variables (optional)

In addition to the required configuration above (ports and file systems), you may also configure the behavior of your cache with the following environment variables:

Variable name Description Defaults
SQUID_IPRANGE Limits the incoming connections to the provided whitelist. By default only standard private network addresses are whitelisted.
SQUID_CACHE_DISK Sets the cache_dir option which determines the disk size squid uses. Must be an integer value, and its unit is MBs. Note: The cache disk area is located at /var/cache/squid. Defaults to 10000.
SQUID_CACHE_MEM Sets the cache_mem option which regulates the size squid reserves for caching small objects in memory. Defaults to "128 MB".

Mount points

In order to preserve the cache between redeployments, you should map the following areas to persistent storage outside the container:

Mountpoint Description Example docker mount
/var/cache/squid This directory contains the cache for squid. See also SQUID_CACHE_DISK above. -v /tmp/squid:/var/cache/squid
/var/log/squid This directory contains the squid logs. -v /tmp/log:/var/log/squid

For more details, see the Frontier Squid documentation.

Configuration customization (optional)

More complicated configuration customization can be done by mounting .sh and .awk files into /etc/squid/customize.d. For details on the names and content of those files see the comments in the customization script and see the upstream documentation on configuration customization.

Running a Frontier Squid Container

To run a Frontier Squid container with the defaults:

[email protected] $ docker run --rm --name frontier-squid \
             -v <HOST CACHE PARTITION>:/var/cache/squid \
             -v <HOST LOG PARTITION>:/var/log/squid \
             -p <HOST PORT>:3128 opensciencegrid/frontier-squid:release

You may pass configuration variables in KEY=VALUE format with either docker -e options or in a file specified with --env-file=<FILENAME>.

Running a Frontier Squid container with systemd

An example systemd service file for Frontier Squid. This will require creating the environment file in the directory /opt/xcache/.env.


This example systemd file assumes <HOST PORT> is 3128 and <HOST CACHE PARTITION> is /tmp/squid and <HOST LOG PARTITION> is /tmp/log.

Create the systemd service file /etc/systemd/system/ as follows:

Description=Stash Cache Container

ExecStartPre=-/usr/bin/docker stop %n
ExecStartPre=-/usr/bin/docker rm %n
ExecStartPre=/usr/bin/docker pull opensciencegrid/frontier-squid:release
ExecStart=/usr/bin/docker run --rm --name %n --publish 3128:3128 -v /tmp/squid:/var/cache/squid -v /tmp/log:/var/log/squid --env-file /opt/xcache/.env opensciencegrid/frontier-squid:release


Enable and start the service with:

[email protected] $ systemctl enable
[email protected] $ systemctl start

Validating the Frontier Squid Cache

The cache server functions as a normal HTTP server and can interact with typical HTTP clients, such as curl or wget. Here, <HOST PORT> is the port chosen in the docker run command, 3128 by default.

[email protected] $ export http_proxy=http://localhost:<HOST PORT>
[email protected] $ wget -qdO/dev/null 2>&1 | grep X-Cache
X-Cache: MISS from 797a56e426cf
[email protected] $ wget -qdO/dev/null 2>&1 | grep X-Cache
X-Cache: HIT from 797a56e426cf

Registering Frontier Squid

See the Registering Frontier Squid instructions to register your Frontier Squid host.

Getting Help

To get assistance, please use the this page or contact directly.