c_ares

This is the resolver based on c-ares dns library.

The following common keys are supported:

• graceful_stop_wait

• protective_query_timeout

• positive_min_ttl

• positive_max_ttl

• negative_min_ttl

server

optional, type: str | seq

Set the nameservers if you do not want to use those in /etc/resolv.conf.

For str value, it may be one or more sockaddr str joined with whitespace characters.

For seq value, each of its value should be sockaddr str.

The default port 53 will be used, if not port is specified in the value string.

Servers in different address families can be set in together.

each_timeout

optional, type: int, unit: ms

The number of milliseconds each name server is given to respond to a query on the first try. After the first try, the timeout algorithm becomes more complicated, but scales linearly with the value of timeout.

default: 2000

Changed in version 1.7.27: change default value from 5000 to 2000 to match default values set in c-ares 1.20.1

each_tries

optional, type: int

The number of tries the resolver will try contacting each name server before giving up.

default: 3

Changed in version 1.7.27: change default value from 2 to 3 to match default values set in c-ares 1.20.1

max_timeout

optional, type: int, unit: ms

The upper bound for timeout between sequential retry attempts. When retrying queries, the timeout is increased from the requested timeout parameter, this caps the value.

notes: This will only have effect if link or build with c-ares 1.22.

default: 0, which is not explicitly set

Added in version 1.7.35.

udp_max_quires

optional, type: int

The maximum number of udp queries that can be sent on a single ephemeral port to a given DNS server before a new ephemeral port is assigned.

notes: This will only have effect if link or build with c-ares 1.20.

default: 0, which is unlimited

Added in version 1.7.35.

round_robin

optional, type: bool

If true, perform round-robin selection of the nameservers configured for the channel for each resolution.

default: false

socket_send_buffer_size

optional, type: u32

Set the send buffer size for the socket.

default: not set, which should be the value of /proc/sys/net/core/wmem_default

socket_recv_buffer_size

optional, type: u32

Set the recv buffer size for the socket.

default: not set, which should be the value of /proc/sys/net/core/rmem_default

bind_ipv4

optional, type: ipv4 addr str

Set the IPv4 bind ip for the resolver while setting up sockets.

bind_ipv6

optional, type: ipv6 addr str

Set the IPv6 bind ip for the resolver while setting up sockets.