Steps to reproduce:
- Install Zabbix Proxy 5.0.14 on OEL 7.7 (kernel 4.14)
- Install Zabbix Server 5.0.14 (in test CentOS 8 was used)
- Register Zabbix Proxy on the Zabbix Server
- Install 2x local DNS servers (in test CentOS 8 + Dnsmasq were used)
- Register Zabbix Proxy's DNS name on both DNS servers for resolving into local private IP
- Set the 2 DNS servers in the Zabbix Proxy's "reolv.conf" so that Zabbix Proxy would resolve DNS names via those 2 local DNS servers (including Proxy's own DNS name)
- In the Zabbix frontend create 7-10 hosts for Zabbix proxy with Agent interface configured with Zabbix Proxy's DNS name registered on the 2 local DNS Servers.
- Set those 7-10 Proxy host instances to be monitored via Zabbix Proxy itself
- Stop the "dnsmasq" service on the first local DNS server
- Observe the queue growing on the server
So in case the first DNS server becomes unavailable host checks by DNS name become slow and queue starts to grow.