Use merged ocelot.json directly from memory instead of from file

[ebjornset]

New Feature

The ConfigurationBuilderExtensions.AddOcelot method merges the ocelot.*.json files into one ocelot.json file that is written back to disk and then added to the IConfigurationBuilder.

Would it be possible to make another AddOcelot method that adds the merged JSON directly from memory into the IConfigurationBuilder using builder.AddJsonStream instead?

Motivation for New Feature

From time to time we experience a problem at startup where something prevents the server process from writing the merged ocelot.json back to disk. When this happens we get an UnauthorizedAccessException (example below) at startup and the process must be killed.

We have not been able to see a consistent pattern in the behavior, and we don't have access to the server since IT operation is outsourced, so this is very hard to debug.

Exception System.UnauthorizedAccessException

Access to the path C:\Octopus\Applications\Dev\Xxxxxxxx\20200429.1_5\ocelot.json is denied.

   at System.IO.File.WriteAllText(String path, String contents)
   at Ocelot.DependencyInjection.ConfigurationBuilderExtensions.AddOcelot(IConfigurationBuilder builder, String folder, IWebHostEnvironment env)
   at Xxxxxxxx.Program.<>c.<CreateHostBuilder>b__1_2(WebHostBuilderContext hostingContext, IConfigurationBuilder config)
   at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass8_0.<ConfigureAppConfiguration>b__0(HostBuilderContext context, IConfigurationBuilder builder)
   at Microsoft.Extensions.Hosting.HostBuilder.BuildAppConfiguration()
   at Microsoft.Extensions.Hosting.HostBuilder.Build()`

[pablo0219]

I really believe that this issue is very important. I'm experimenting this issue when deploying to an App Service in Azure. I have different microservices and ocelot.json is overridden every time. Of course, I'm getting UnauthorizedAccessException. I know, Ocelot was thought first for containers, but that approach has its own challenges when working in development. I think, Ocelot shouldn't change ocelot.json in any way (should be kept in memory) and if some kind of persistence needs to be done, it should be in some kind of DB.

[raman-m]

@ebjornset commented on Apr 29, 2020

Eirik,
Thanks for your interest in Ocelot!

I believe this feature will be a great enhancement of Ocelot core.
Yeah, merging configs to a file works in non-virtual environments like IIS, Kestrel, Docker where we have real file system.
You've pointed the attention to virtual environments like all cloud providers like AWS, Azure and GCP.

My opinion, it would be better to introduce a feature switch between non-virtual and virtual environments to control file system and config merging. And, right, merging in a memory will be an option, for sure.

Also, pay attention we have some PRs which are similar to your one, because they solve the same problematic by merging in a memory. See the following:

• #651 Merge custom properties of config file #1183

Let's discuss more...

[raman-m]

@pablo0219 commented on Jun 10, 2020

Hi Pablo!
Thanks for your ideas!

I'm not sure about DB usage here for this issue. But you are welcome to create new PR to present real implementation which will use DB decoupling by interface.

And, yes, in any virtual environment (all cloud providers) we have virtual file system, and finally we get the exception you've mentioned.
My suggestion is decoupling of file operations by introducing a new file service which must handle all real and virtual file operations to abstract on file storage. And that must solve the problem with exceptions during operations of file system.
And for sure, we have to implement file storages components for all cloud providers.

Your opinion here?

[raman-m]

+ Accepted

...due to ready PR #1227

[raman-m]

@ebjornset @pablo0219
Are you online?
Are you still with Ocelot?
If Yes, could you review current code of #1227 plz? Any your feedback is welcome!