Bug 1772593

This bug was initially created as a copy of Bug #1684079

I am copying this bug because: 
Backport request 4.1.
I'll do the backport myself


Description of problem:

Customer has 15  egressNetworkpolicies, with 479 rules, of which 150 are dnsName. Most of these dnsName are repeated:
$ cat enp.txt | grep namespace: -c
15
$ cat enp.txt | grep -c -- '- to'
479
$ cat enp.txt | grep dnsName: | wc -l
150
$ cat enp.txt | grep dnsName: | sort -u | wc -l
17

This causes a severe performance issue because dig is being called constantly.

The egressNetworkPolicy checks for the dnsName A record TTL calling dig, as dig calls dnsmasq the first time this dig is called, dnsmasq returns the TTL, the second time it returns TTL - time elapsed since the previous query.

If an A record has a very small TTL (i.e. github.com has only 60 seconds) there will be a lot of digs called making things even worse.

Customer has 14 entries for github.com:
$ cat enp.txt | grep 'dnsName: github.com' -c
14

I asked the customer to use execsnoop ( https://github.com/iovisor/bcc/blob/master/tools/execsnoop.py ) and I see in 10.283 seconds 82 occurences of "/usr/bin/dig +nocmd +noall +answer +ttlid a github.com"

In those 10.283 seconds I also see dig being called 1038 seconds by atomic-openshift-node pretty evenly distributed:

$ for i in {0..9}; do cat digsnoop | grep -v ^10 | grep -c ^$i; done
72
135
143
103
81
126
89
83
63
104

Version-Release number of selected component (if applicable):
3.9, but I don't see any relevant change in 3.11 so it probably affects both

How reproducible:
Always

Steps to Reproduce:
1. Create several egressNetworkPolicy objects in several projects pointing to the same hostnames. Use at least 10 different hostnames and make sure the A record has a low TTL (25 is pretty low)
2. Wait two minutes so that the caches start refreshing

Actual results:
dig is called several times per second

Expected results:
Dig is called once every TTL for all the rules

Additional info:
Calling dig so often on every node has a big performance impact.