Why not use "blocking queries" with Consul?

[SnailDev]

Expected Behavior / New Feature

Many endpoints in Consul support a feature known as "blocking queries". A blocking query is used to wait for a potential change using long polling. Not all endpoints support blocking, but each endpoint uniquely documents its support for blocking queries in the documentation.

Blocking Queries could notify ocelot the latest configuration immediately (when store configuration in consul) and the latest health services immediately(when service discovery and load balancer).

[SnailDev]

I have read source of ocelot, with test, and I found if use service discovery and load balancer, ocelot will get health reroute server every request and it will affect performance. So I think memorycache and block queries would be useful.

[TomPallister]

@SnailDev Thanks for your interest in the project. This sounds good, I don't know if the .net package I used to talk to Consul supports this blocking queries model you mention.

The performance impact of calling consul on every request is tiny because you should be calling consul agent as a sidecar on localhost. Yes there is a cost associated with this and polling consul for the services is a good idea and has been on my todo list for a long time!

If you would like to have a go at implementing this change I'm happy to accept a PR!

[TomPallister]

I have merged a new feature that will allow users to specify if they want to poll consul

[TomPallister]

Released in 7.0.5

[SnailDev]

@TomPallister I have read your solution. but there are two problems:

1. PollingConsulServiceDiscoveryProvider init on the first request and _timer poll services from consul, so the first request will be fail.
2. _timer poll just run once. I logged in poll method and I found the log print just on first request.

private async Task Poll()
{
    _logger.LogInformation("Started polling consul");
    _services = await _consulServiceDiscoveryProvider.Get();
     _logger.LogInformation("Finished polling consul");
}

please confirm it, thank you very much.

[SnailDev]

@TomPallister by the way, may be you need to take some time to know block queries, more detail: https://www.consul.io/api/index.html ， and you use consuldotnet in ocelot with consul, This API also assumes some knowledge of Consul, including things like blocking queries and consistency modes

[TomPallister]

@SnailDev cool!!! It's not high on priority list at the moment but I would be happy to accept a PR if you want a challenge!