[kea-dev] Lease File Cleanup in Kea - Design Document

[Chaigneau, Nicolas]

Hello Marcin,


A point which I forgot to address, regarding the "concurrent runs" issue:

"The kea-lfc implements locking using the PID file to prevent concurrent runs. When the kea-lfc is started, it checks for the presence of the PID file. If the file exists, it checks if the process with a PID from the PID file is running. If the process is running, the application terminates. If the PID file doesn't exist or the process with a given PID is not running, the kea-lfc creates a new PID file with its own PID and continues to run."


Several kea servers may run on a single host, each having its own separate configuration.
Consequently, kea-lfc must also be allowed to run concurrently (one instance of kea-lfc matching each instance of kea).
To allow this, the PID file should be configurable. I think the logical place would be in kea's configuration file. 



Regards,
Nicolas.


> All,
> 
> I have updated the Lease File Cleanup design with the comments from Stephen and Tomek (see ticket #3685). You may want to have a look and see if there is anything glaring. Minor comments like: spelling errors, some naming conventions may also be useful but they have little chance of being applied by the 0.9.1 release.
> 
> The major change (which was actually applied in the LFC requirements
> document): http://kea.isc.org/wiki/LeaseFileCompressionRequirements is the removal of the following requirement:
> 
> "b. The LFC should not remove the contents of the lease file which is not identified as a lease information or is an invalid lease information."
> 
> Although, I initially thought it would be a useful capability, I now tend to think that it is not worth the effort for the following reasons:
> - We don't support comments in the lease files, and I don't think that supporting them really makes any sense, because lease file is not meant to be edited manually
> - If the server crashes when it is writing a lease into the lease file, and the lease information is incomplete, the server could rewrite the incomplete lease to the new file. But, how this incomplete entry would be fixed? Manually? By that time the client would probably return and get its lease back.
> 
> However, the most important point is that implementation of this capability would require tracking the position of the unparsable data in the source lease file so as it will be rewritten in the same position (e.g. between lease X and Y) in the output file. At the same time, the updated LFC algorithm now loads all leases into memory, instead of reading and writing them one-by-one which makes it troublesome to match the position of the particular piece of unparsable information within the lease data structure, because current data structures do not support this capability.
> 
> Please read the design document: http://kea.isc.org/wiki/LFCDesign and report issues on the mailing list.
> 
> Marcin
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