Resolver in Kubernetes

[rjshrjndrn]

Hi lua noobie here,
First of all, thank you for this awesome plugin.
I have headless services(DNS resolution will give all service's ips) in Kubernetes and want to have sticky sessions on that. Unfortunately, this is not possible with Nginx OSS. So while looking through openresty, I've found this plugin.

As of now, I use resolver=local (in openresty) settings in Kubernetes, because it'll work on any Kubernetes cluster the app gets installed. Now the issue is, is there any way not to give static DNS resolver addresses?

for example, in this code

 master_dns = dns_resolver.new_master{
      cache = "dns_cache", upstream_domain = "upstream.ddnsr-demo.com", dns_servers = {"172.20.0.2"}
    }

Is there any way to avoid the 172.20.0.2 ?

Any help is appreciated.

[jkeys089]

@rjshrjndrn If you're using a local resolver then I believe you're relying on the local resolve.conf file to lookup IP's. This lib doesn't support that feature directly -- we currently only support querying a DNS server. I'm not sure if there is a convenient workaround in Kubernetes but you could possibly use something like dnsmasq which supports reading from your local resolve.conf and responds to DNS queries.

[rjshrjndrn]

Oh.. That's a blocker. But thanks for that pointer. One more thing. Can I get the complete list of ips as an array or something like that, rather than a single ip.

What I'm trying to achieve is sticky sessions for headless service(dns query for that service will give all ip addresses). So thought I can offload the ips to another module. For example, pass the complete array to this function.
https://github.com/openresty/lua-resty-balancer#synopsis

I don't know how practical that'll be because I am super noob in playing with lua

[jkeys089]

@rjshrjndrn I'm not sure I fully understand what you're trying to accomplish. If you just want to know all IP's you can get them using client. _hosts. To ensure everything is sync'ed properly you should probably execute client:get() first.

[rjshrjndrn]

I've one application which does some session affinite things. I've created a headless service for that

root@ngx-54846c7555-2d2z8:/# dig headerecho.app.svc.cluster.local

; <<>> DiG 9.11.5-P4-5.1+deb10u6-Debian <<>> headerecho.app.svc.cluster.local
;; global options: +cmd
;; Got answer:
;; WARNING: .local is reserved for Multicast DNS
;; You are currently testing what happens when an mDNS query is leaked to DNS
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 54723
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: d1116855f9cc9212 (echoed)
;; QUESTION SECTION:
;headerecho.app.svc.cluster.local. IN   A

;; ANSWER SECTION:
headerecho.app.svc.cluster.local. 2 IN  A       10.42.0.112
headerecho.app.svc.cluster.local. 2 IN  A       10.42.0.113

;; Query time: 0 msec
;; SERVER: 10.43.0.10#53(10.43.0.10)
;; WHEN: Thu Feb 24 07:32:44 UTC 2022
;; MSG SIZE  rcvd: 169

I want whenever http://nginx.app.cluster.svc.local/header is called from 1 ip, it should always go to either pod1 or pod 2. Not round robin.

I hope now it's clear.

Can you gimme some suggestions on this problem?

Any help is much appreciated.

[jkeys089]

@rjshrjndrn perhaps https://github.com/Kong/lua-resty-dns-client is what you're looking for?

[rjshrjndrn]

Thank you very much @jkeys089. But as I told you earlier I'm a super noob in lua. That library seems to be from scratch build type. There is no getting started/sample snippets to get started also... But thanks for the direction. Much appreciate it :)