Support app_offline.htm

[Tratcher]

• Deployer uploads app_offline.htm (case insensitive)
  • HPH serves app_offline.htm for any new incoming requests
• HPH signals process shutdown (SignalR, WebSockets) (opt-in web.config: signalShutdown=true ?)
  • Ctl+C https://msdn.microsoft.com/en-us/library/ms683155(v=vs.85).aspx
  • Ctl+Break? Can Hosting receive both of these? Break might be more correct.
  • General feature for graceful shutdown
• HPH waits for process to end with timeout if shutdown signal was requested&sent
• Deployer needs to find out when the process is down / the files are unlocked
  • Retry loop on deletefile?
• Deployer uploads new files
• Deployer deletes app_offline.htm
• HPH restarts the back-end process

Initial HPH work completed by end of Feb.
Deployer developed in parallel
Update publish-iis to add signalShutdown to the web.config

RE: aspnet/Hosting#141
@sayedihashimi

[Tratcher]

Hosting already supports Ctl+C and Ctl+Break.

[muratg]

Cool, thanks for checking!

[muratg]

Note for HPH side: CreateProcess will need to be called the right way with the flag CREATE_NEW_PROCESS_GROUP as specified in the msdn article

[guardrex]

HPH serves app_offline.htm for any new incoming requests

HPH will be checking periodically for the presence of this file? I wish checking for the file file could be disabled in options for app.UseIISPlatformHandler().

[moozzyk]

@guardrex - why?

[guardrex]

Perf concern ... How often does HPH have to check for the file? Is it inconsequential (i.e., milliseconds spent every several seconds ... i.e., that's no "concern" to be concerned about)?

[PureKrome]

@moozzyk

• Some people might never want to push up an app_offline.hml so why waste the cpu check(s) (yes, micro opt).
• Security. disable the option for a rogue person to throw the site offline by just uploading a single file with some hacker message, etc.

edit: @guardrex beat me by about 20 secs. ha doh.

[moozzyk]

@guardrex - Perf concern - I would assume that platform handler will not poll but be notified about changes. Not sure how much overhead it would add but IIS already monitors changes to the web.config file and I don't think this is causing perf issues.

@PureKrome -

Security. disable the option for a rogue person to throw the site offline by just uploading a single file with some hacker message, etc.

I guess this is always true - overwriting the .exe containing the app will have the same effect and you can take the site down just by overriding the web.config file.

[guardrex]

Perf concern - I would assume that platform handler will not poll but be notified about changes.

Perfect! ...... concern withdrawn.

[Tratcher]

@guardrex On a related note, HPH is configured exclusively via the web.config. There's nothing you/we can do once the app has launched. UseIISPlatformHandler and similar just consume things provided by HPH.