Auto update a service
I have written several services in Delphi now, but I want to add the facility of auto updating the service either from a LAN unc path or from a http server. I have been pondering this and I am interested to hear peoples ideas. I can create a thread that will check for the update periodically, but how do I go about stopping the service uninstalling and installing automatically. My initial thoughts where to write a console app to do this and start it using create process, then let the service stop and the console app do the work, starting the new version of the service before it exits. Is this a good stratergy or shoul I consider something else. Thanks in advance
I do as you suggest. A thread checks occasionally for an update. If it is present, it downloads it and puts it into an appropriate place. It then verifies that it is wholesome (don't want it to be broken!). Finally, the thread then launches another app with parameters to tell it what to do, specifically, the name of the service, the location of the file to replace, and the file to replace it with. Then the service just waits.
When the updater app starts, it pauses a moment to make sure that the service is all stable, and then it uses the service control API to stop the service. It then monitors it until it is gone. Finally, it pauses a little to ensure that Windows has really finished with the file. Then it starts the process of renaming the old file to move it out of the way (if still in use, it retries a few times), and then copying the new file into place. And finally, it starts the service up again. Then the updater quits.
This has worked quite reliably for my services, and also standalone apps too (with different parameters for the updater app to know which mode). And if you are careful, you can update the updater using the exact same system, which is nice to watch.
I would have the service be a shell that only updates another executable or DLL file where the real code is at.
Have some communication method between the shell and the child process to force a shutdown and then have the shell perform the upgrade and relaunch the child.
As a side note, this makes debugging the service much easier as well as you'll be able to run the child process directly without having to worry about the extra efforts required to debug windows services.