docker配置DNS详解

背景

有的时候主机的DNS，docker的DNS不想设置一致，或是部分场景需要，或是业务需要，故此有此主题。
默认docker容器的DNS是主机的DNS，那么原本更改主机的DNS就好了,但是运维反馈，腾讯云ECS的DNS会变动（离塞谱），由于没有权限访问一些模块，也没办法排查，找到根因，故此就以docker配置DNS为例，临时解决一下。

环境说明

# lsb_release -a

No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 22.04.3 LTS
Release:        22.04
Codename:       jammy

# docker info
Client: Docker Engine - Community
 Version:    24.0.7
 Context:    default
 Debug Mode: false

# 作为容器DNS测试
docker pull ubuntu:20.04

宿主机 Ubuntu 22.04.3 LTS DNS查看

这台主机用的是内网的DNS

# resolvectl status | grep DNS
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.xx.1
       DNS Servers: 192.168.xx.1
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

扩展内容，如果你需要更改主机的DNS，可以本站搜索 ubuntu22.04更改DNS 找找，应该有一些教程。

启动容器,验证DNS是宿主机的DNS

docker run -itd --name test ubuntu:20.04

docker exec -it test bash

root@76347263090f:/# cat /etc/resolv.conf
# This is /run/systemd/resolve/resolv.conf managed by man:systemd-resolved(8).
# Do not edit.
#
# This file might be symlinked as /etc/resolv.conf. If you're looking at
# /etc/resolv.conf and seeing this text, you have followed the symlink.
#
# This is a dynamic resolv.conf file for connecting local clients directly to
# all known uplink DNS servers. This file lists all configured search domains.
#
# Third party programs should typically not access this file directly, but only
# through the symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a
# different way, replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

nameserver 192.168.xx.1
search .

# 可以看到DNS是宿主机的DNS

修改 Docker 守护进程配置

/etc/docker/daemon.json 中 添加 DNS 配置：

{
  "dns": ["8.8.8.8", "8.8.4.4"]
}

需要重启 docker , systemctl restart docker

root@76347263090f:/# cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4

对单个容器修改DNS

需要重建容器

docker run -itd --name test --dns 8.8.4.4 --dns 114.114.114.114 ubuntu:20.04

docker exec -it test bash

root@b0548e7b21ca:/#  cat /etc/resolv.conf
nameserver 8.8.4.4
nameserver 114.114.114.114

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