Use shared memory

[nicholaschiasson]

Would be better to share jdomain state among all workers in order to save on redundant DNS queries and also keep all workers in sync when an update occurs.

[splitice]

I too think this would be really good as it would prevent the inrush of DNS queries after daemon reload.

Any chance @nicholaschiasson that you are going to look into this. I'm happy to help (although I'm not super familiar with nginx).

[splitice]

I would be happy to make some contributions on other matters however, like getting the tests working again

[nicholaschiasson]

Hi @splitice , unfortunately I haven't had the time to address this. I would appreciate some help for sure. I realized right away with my last change that I broke tests and had been trying to fix that but got sidetracked. If you are willing to help with that of course that would be super appreciated! Just drop a merge request whenever you like.

[atomsnc]

Won't the zone directive present in upstream module do the job here?
http://nginx.org/en/docs/http/ngx_http_upstream_module.html#zone

If you check the function ngx_http_upstream_zone_copy_peers in ngx_http_upstream_zone_module.c, in the end it sets pointer of peers in ngx_http_upstream_srv_conf_t to a pointer backed by shared memory pool.

We don't have to do much on our end. Just need to store the mutex and shpool from ngx_http_upstream_rr_peers_t
during ngx_http_upstream_init_jdomain (in instance struct I would say) and then use something like ngx_http_upstream_rr_peers_wlock and ngx_http_upstream_rr_peers_unlock for the stored shared pool during ngx_http_upstream_jdomain_resolve_handler while updating the peers.

At that point, instance struct should probably be moved to shared memory pool as well (shpool).

[atomsnc]

Looks like shared memory pool has init after the modules configuration init where upstream module called upstream_init. So the pointers copied by jdomain won't be the shared ones.