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The Frontier distributed database caching system distributes data from data sources to many clients around the world. The name comes from "N Tier" where N is any number and Tiers are layers of locations of distribution. The protocol is http-based and uses a RESTful architecture which is excellent for caching and scales well. The Frontier system uses the standard web caching tool squid to cache the http objects at every site. It is ideal for applications where there are large numbers of widely distributed clients that read basically the same data at close to the same time, in much the same way that popular websites are read by many clients.

For Large Hadron Collider (LHC) projects, the database is located at the CERN Tier 0, and the Frontier system distributes data to to all the Tier 1, Tier 2, and Tier 3 sites around the world. Within each site the Frontier system also distributes the data to all the worker nodes (typically hundreds or thousands) that need to read the data.

The Frontier system was developed for the CDF experiment at Fermilab and is heavily used there. Fermilab also adapted Frontier for the CMS experiment at the LHC at CERN and it is used to access "conditions data" (mainly detector calibrations and alignments) at all its sites worldwide. The ATLAS experiment at the LHC later also adopted Frontier to distribute conditions data to all of its sites.

Even though this web site is hosted at CERN for convenience of the LHC projects, Frontier is maintained by Fermilab. The LHC projects choose the level of abstraction between client and server to be SQL queries, but the Frontier system is designed with plugins so applications can put more of the logic on the server side, and that is how CDF uses it. There is also a plugin that reads from files on the local disk or other http web servers. The main advantage of using Frontier instead of directly using a http web server and squid proxy is that years of experience have resulted in Frontier supplying many features that are important for robust and flexible operation on computing grids. A summary of the features and components of the Frontier system is available in this overview webpage.

Source code and other project information for frontier client (implemented in C and C++) and frontier server (implemented as a java tomcat servlet) is freely available as open source, mostly under the Fermilab Fermitools license (a BSD license). Here are instructions for deploying squid for CMS and instructions for deploying squid for ATLAS. Here's a brief introduction to the CMS Frontier architecture.

These are the CMS Offline Frontier monitoring systems: This is the CMS Online Frontier monitoring systems (awstats & MRTG)
These are the ATLAS Frontier monitoring systems:

The monitoring for the squids that back the Frontier infrastructure are now federated under the WLCG banner. The WLCG Squid Monitoring service is performing monitoring of squids for CMS, ATLAS and CVMFS (a non-Frontier related WLCG service). Find below a list of relevant links

The monitoring pages for the CVMFS servers can be found at the CVMFS traffic pages (awstats).

For general discussions about Frontier subscribe to the frontier-talk mailing list. If you don't have a CERN account, on the login screen click on Create/Check your account and register for a Lightweight Account in the lower right corner. Once you're logged in, click on the 'Join/leave group' link to the right of the frontier-talk search result.

If you have support questions for CMS or ATLAS Frontier, send a message to one of these:

(these are images to prevent spam so you can't click on them or copy/paste them, sorry).

For more information about Frontier visit the CMS DatabaseAccess TWiki page.

Some publications about Frontier: