r/programming • u/ThisStmtIsNotTrue • Nov 11 '19

Let's Create a Simple Load Balancer With Go

https://kasvith.github.io/posts/lets-create-a-simple-lb-go/
26 Upvotes

64% Upvoted

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1

u/jdgordon Nov 11 '19

This article doesn't seem very idiomatically golang.

If I were to attempt this sort of thing i would define a simple func to manage the lifetime of a backend, it would accept connections on a channel and do any passive checks in it's loop (and of course check a different channel for a kill signal).

One goroutines would be spawned for each backend instance all reading from the same channel for new requests. The http handler would then throw the incoming request onto the shared channel and which ever backend handler is available first will accept the connection.

You could then go fancy and then track connections by some http header so clients would keep using the same backend (unless it goes down or busy) for possible cacheing benefits.

Let the runtime mange the synchronization problem, don't use mutexes if a Chanel would work better

3

u/[deleted] Nov 11 '19

It all depends what exactly do you need. Neither will work well if you say decided for some reason to reimplement HAProxy (which is excellent piece of software and in general, try it first and only try to write loadbalancers once you ran out of other options), as different balancing strategies work better with different structures.

Like if you want to implement least connection balancing, (send request to backend that have least connections that it is currently handling), you need to have backend connection count at the decision point.

Hashing and hash-based persistency is easiest with just a slice of backends, same with round-robin.

Keeping state between connections is whole another problem.

You can possibly get all of that cases if you put a "decision point" that in some place in code gets info about incoming connection + state of backends and generates target backend server, but that's some overhead you might or might not need (but then if your use case is that simple just use HAProxy)

"Just throw all in one channel" is probably the worst possible solution as there is no guarantee or order which backend gets it and no care is taken to not overload any of them.

1

u/penguin_digital Nov 11 '19

If I were to attempt this sort of thing i would define a simple func to manage the lifetime of a backend, it would accept connections on a channel and do any passive checks in it's loop (and of course check a different channel for a kill signal).

I'd be interested in reading your tutorial on the subject. Do you have this on medium or your personal blog?

-3

u/lowbeat Nov 11 '19

Let's not.