HttpClientFactory with HttpPolly Proof of Concept
The purpose of this POC is to demonstrate how to add resiliency to intercommunications between micro-services and also to demonstrate that the use of other tools such as RestEase or Refit can be used seamlessly in tandem with HttpClientFactory and HttpPolly.
Documentation References
| Title | Link |
|---|---|
| Microsoft Docs | https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-2.2#use-polly-based-handlers |
| Refit Repository | https://github.com/reactiveui/refit |
| Polly (Dynamic Policy Reconfiguration) | https://github.com/App-vNext/Polly/wiki/Dynamic-reconfiguration-during-running |
| Polly (Bulkhead) | https://github.com/App-vNext/Polly/wiki/Bulkhead |
| Polly (Policy Wrap) | https://github.com/App-vNext/Polly/wiki/PolicyWrap |
| Delegating Handler Order | https://www.stevejgordon.co.uk/httpclientfactory-aspnetcore-outgoing-request-middleware-pipeline-delegatinghandlers |
| Simulate Response Codes | https://httpstat.us/ |
Starting the POC
This is a simple console application that can be started up without any extra effort. When it starts, the console will open and a lot of output will flood. Look for the "warning" type messages that are written in all caps for test begin sections.
Things I Learned
- It's best to just add new policies to the registry.
- Working with policy handlers is a lot like working with middleware - first in, last out.
- Certain policies are state-ful and apply to the entire client regardless of the call.
- IHttpClientFactory manages the HttpClient lifetime now and we no longer have to worry about having a single HttpClient, but you can set a custom lifetime on your client.
- IHttpClientFactory supports typed clients which both RestEase and Refit can be used to provide.
- There's a site out there to return simulated response codes
- Microsoft's HttpClientFactory is extremely flexible and works great with HttpPolly, RestEase, and Refit.
- Refit has a ton of features and you can just read about them here - because that's not what this POC is for... ;)
Things I'm Still Not Sure About
- Are MessageHandlers and PolicyHandlers treated the same when it comes to order of execution?
- How can you change the policy configuration during runtime when using the policy registry?
Things You Probably Didn't Notice
- There's a period missing from a sentence above.