Skip to content

Install the Frontier Squid HTTP Caching Proxy

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 distributed computing 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.

This document is intended for System Administrators who are installing frontier-squid, the OSG distribution of the Frontier Squid software.

OSG recommends that all sites run a caching proxy for HTTP and HTTPS to help reduce bandwidth and improve throughput. To that end, Compute Element (CE) installations include Frontier Squid automatically. We encourage all sites to configure and use this service, as described below.

For large sites that expect heavy load on the proxy, it is best to run the proxy on its own host. If you are unsure if your site qualifies, we recommend initially running the proxy on your CE host and monitoring its bandwidth. If the network usage regularly peaks at over one third of the bandwidth capacity, move the proxy to a new host.

Before Starting

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

  • Hardware requirements: If you will be supporting the Frontier application at your site, review the hardware recommendations to determine how to size your equipment.
  • User IDs: If it does not exist already, the installation will create the squid Linux user
  • Network ports: Clients within your cluster (e.g., OSG user jobs) will communicate with Frontier Squid on port 3128 (TCP). Additionally, central infrastructure will monitor Frontier Squid through port 3401 (UDP); see this section for more details.

As with all OSG software installations, there are some one-time (per host) steps to prepare in advance:

Installing Frontier Squid

To install Frontier Squid, make sure that your host is up to date before installing the required packages:

  1. Clean yum cache:

    root@host # yum clean all --enablerepo=*
  2. Update software:

    root@host # yum update

    This command will update all packages

  3. Install Frontier Squid:

    root@host # yum install frontier-squid

Configuring Frontier Squid

Configuring the Frontier Squid Service

To configure the Frontier Squid service itself:

  1. Follow the Configuration section of the upstream Frontier Squid documentation.
  2. Enable, start, and test the service (as described below).
  3. Register the squid (also as described below).


An important difference between the standard Squid software and the Frontier Squid variant is that Frontier Squid changes are in /etc/squid/ instead of /etc/squid/squid.conf.

Configuring the OSG CE

To configure the OSG Compute Entrypoint (CE) to know about your Frontier Squid service:

  1. On your CE host (which may be different than your Frontier Squid host), edit /etc/osg/config.d/01-squid.ini

    • Make sure that enabled is set to True
    • Set location to the hostname and port of your Frontier Squid service (e.g.,
    • Leave the other settings at DEFAULT unless you have specific reasons to change them
  2. Run osg-configure -c to propagate the changes on your CE.


You may want to finish other CE configuration tasks before running osg-configure. Just be sure to run it once before starting CE services.

Using Frontier-Squid

Start the frontier-squid service and enable it to start at boot time. As a reminder, here are common service commands (all run as root):

To... Run the command...
Start the service systemctl start frontier-squid
Stop the service systemctl stop frontier-squid
Enable the service to start on boot systemctl enable frontier-squid
Disable the service from starting on boot systemctl disable frontier-squid

Validating Frontier Squid

As any user on another computer, do the following (where <MY.SQUID.HOST.EDU> is the fully qualified domain name of your squid server):

user@host $ export http_proxy=http://<MY.SQUID.HOST.EDU>:3128
user@host $ wget -qdO/dev/null 2>&1|grep X-Cache
user@host $ wget -qdO/dev/null 2>&1|grep X-Cache

If the grep doesn't print anything, try removing it from the pipeline to see if errors are obvious. If the second try says MISS again, something is probably wrong with the squid cache writes. Look at the squid access.log file to try to see what's wrong.

Registering Frontier Squid

To register your Frontier Squid host, follow the general registration instructions here with the following Frontier Squid-specific details. Alternatively, contact us for assistance with the registration process.

  1. Add a Squid: section to the Services: list, with any relevant fields for that service. This is a partial example:

        Description: Generic squid service

    Replacing <FULLY QUALIFIED DOMAIN NAME> with your Frontier Squid server's DNS entry or in the case of multiple Frontier Squid servers for a single resource, the round-robin DNS entry.

    See the BNL_ATLAS_Frontier_Squid for a complete example.

  2. Normally registered squids will be monitored by WLCG. This is strongly recommended even for non-WLCG sites so operations experts can help with diagnosing problems. However, if a site declines monitoring, that can be indicated by setting Monitored: false in a Details: section below Description:. Registration is still important for the sake of excluding squids from worker node failover monitors. The default if Details: Monitored: is not set is true.

  3. If you set Monitored to true, also enable monitoring as described in the upstream documentation on enabling monitoring.

A few hours after a squid is registered and marked Active (and not marked Monitored: false), verify that it is monitored by WLCG.



The frontier-squid installation will create one user account unless it already exists.

User Comment
squid Reduced privilege user that the squid process runs under. Set the default gid of the "squid" user to be a group that is also called "squid".

The package can instead use another user name of your choice if you create a configuration file before installation. Details are in the upstream documentation Preparation section.


Open the following ports on your Frontier Squid hosts:

Port Number Protocol WAN LAN Comment
3128 tcp Also limited in squid ACLs. Should be limited to access from your worker nodes
3401 udp Also limited in squid ACLs. Should be limited to public monitoring server addresses

The addresses of the WLCG monitoring servers for use in firewalls are listed in the upstream documentation Enabling monitoring section.

Frontier Squid Log Files

Log file contents are explained in the upstream documentation Log file contents section.

Back to top