DNS Cache Update¶

The DNS cache update feature allows you to make asynchronous DNS requests and cache results for a configured period of time. This feature could be useful when DNS load balancing is used.

Feature availability

This feature and corresponding variables are supported only in the PROXY API Firewall mode.

To configure the DNS cache update, use the following environment variables:

Environment variable	Type	Description
`APIFW_DNS_CACHE`	`bool`	Turns on using async DNS resolving and caching feature. The default value is `false`.
`APIFW_DNS_FETCH_TIMEOUT`	`time.Duration`	TTL of the cache. The default value is `1 minute`.
`APIFW_DNS_LOOKUP_TIMEOUT`	`time.Duration`	Lookup timeout. The default value is `1 second`.
`APIFW_DNS_NAMESERVER_HOST`	`string`	Host of the custom nameserver. By default the value is `“”`. In this case the configured in the system DNS server will be used.
`APIFW_DNS_NAMESERVER_PORT`	`string`	Port of the custom nameserver. The default value is `53`.
`APIFW_DNS_NAMESERVER_PROTO`	`string`	Protocol to use. Possible values are case `tcp`, `tcp4`, `tcp6`, `udp`, `udp4`, `udp6` - `4` and `6` are IPv4 and IPv6. The default value is `udp`.

When the asynchronous DNS resolving and caching feature is turned on, a dedicated goroutine is started and the DNS cache is updated every fetch timeout period. If a custom nameserver is configured then it will be used by the APIFW for all requests and DNS caching system. If a host contains multiple IPs for one entry then the first entry will be used. Also, the IPv4 has higher priority than the IPv6 IPs.