Releases and ChecksumsPosted on April 13th, 2012
Big sympathies for my peers and compatriots over at Bioware Austin today. The live SW:TOR servers are down for the next seven hours or so after a deployment issue resulted in old data pushed live. Since I’m not there, I can’t make any kind of informed guess as to exactly how this happened. They’ve said they need to rebuild assets; the time span for this fix is the combination of however long it takes to do the rebuild and however long it takes to push the new assets out to all their servers. Both of these are potentially time-consuming. Eight hours makes me think they need to rebuild a large chunk of the data from scratch.
In general, I recommend implementing a checksum into your push process and server startup scripts. Before you fire up a server binary, you should run a checksum (maybe Fletcher or Adler-32) on your binaries and your data files, and make sure they match what’s expected for that build. If they don’t match, throw an error and don’t run the binary.
There are potential speed issues here if your data is large. You can speed up the process by calculating the checksum for a smaller portion of each file, or you could be a little more daring and just compare file names and sizes. Bear in mind that you’re trying to compensate for failures of the release system here, though, so you wouldn’t want to rely only on simple checks.
Also, if you’re looking at checksums which were also generated by the build system, you need to account for the possibility that those checksums are wrong. Single points of failure can occur in software as well as hardware.
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