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| -rw-r--r-- | src/bin/lfc/lfc.dox | 80 |
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diff --git a/src/bin/lfc/lfc.dox b/src/bin/lfc/lfc.dox new file mode 100644 index 0000000..769a3ff --- /dev/null +++ b/src/bin/lfc/lfc.dox @@ -0,0 +1,80 @@ +// Copyright (C) 2015-2018 Internet Systems Consortium, Inc. ("ISC") +// +// This Source Code Form is subject to the terms of the Mozilla Public +// License, v. 2.0. If a copy of the MPL was not distributed with this +// file, You can obtain one at http://mozilla.org/MPL/2.0/. + +/** + @page lfc Lease File Cleanup Component + +The Lease File Cleanup component (kea-lfc) is a service process that removes redundant +information from the files used to provide persistent storage for the memfile data base +backend. + +When using the memfile database backend Kea servers store persistent lease information +in lease files. They add new lease information to the file by appending it to the end +of the file. In a typical lease file you might find several instances of the same lease, +one for each time the client acquired or renewed the lease. In order to remove this +redundant information and to keep the lease files from growing without bound the +Kea servers will periodically run kea-lfc. This process will read the leases from +the lease files and keep only the most recent instance of each lease. When it finishes +reading the leases it will write the unique leases to the output file. + +The design documentation for kea-lfc can be found here: +<a href="https://gitlab.isc.org/isc-projects/kea/wikis/Lease-File-Cleanup-design"> LFC Design</a> + +While kea-lfc can be started externally, there is usually no need to do this as the +Kea servers will run it on a periodic basis. + +@section lfcProcessing Processing +kea-lfc operates on a set of files, using them for input and output +of the lease entries and to indicate where it is in the process in case of an +interruption. Currently the caller must supply names for all of the files, in +the future this requirement may be relaxed with the process getting the names +from either the config file or from defaults. + +kea-lfc is built on the isc::lfc::LFCController class. Effectively this provides +a single external routine, isc::lfc::LFCController::launch, which is called with +the arguments from the command line and proceeds to parse the arguments and +then process the lease files. + +It uses isc::util::PIDFile to manipulate a PID file to mediate access to the +leases. When a new process is started it will check the PID file. If the +PID file exists and a process with that ID is still running already the new +process will be terminated. If no other process is running the PID of the +new process is written to the file. + +It uses the isc::dhcp::LeaseFileLoader class to first read all of the leases +into either isc::dhcp::Lease6Storage or isc::dhcp::Lease4Storage containers. +The leases are read in the order they were written to the file and younger leases +overwrite older leases for the same address. When the process finishes reading +the lease files there will be a single lease entry for each address used. At +this point the process again uses the isc::dhcp::LeaseFileLoader class to write +an entry for each remaining lease into the output file. + +Lastly kea-lfc moves the files to indicate completion (see below) and removes +the extra files then exits. + +@section lfcFiles File Manipulation + +This section is intended to provide a brief overview of how kea-lfc uses its +files. For a more in depth discussion of the design see +<a href="https://gitlab.isc.org/isc-projects/kea/wikis/designs/Lease-File-Cleanup-design">LFC Design</a> + +There are four files used during the kea-lfc process: previous, input, output +and finish. They are used to both hold the leases and to indicate to the Kea +servers and to other instances of kea-lfc what processing has been completed. + +The previous file is the result of a previous run of the kea-lfc process. + +The input (or copy) file is created by the kea server just before invoking +the kea-lfc process. The kea server will move it's current lease file to +the input file and then start using a new current file. + +The output file is created by kea-lfc as it writes the leases to a file. When +kea-lfc finishes writing all the leases to the output file it renames the output +file to be the finish file. It then removes the previous and input files and +renames the finish file to be the previous file. + +*/ + |