英文:
Cant connect to docker container port of some images
问题
尝试调查我的 Docker 容器问题。我曾花了一整天认为问题出在 Node.js 代码中（它有一个服务器，我试图连接到这个服务器）。
经过调查，我发现了对我来说很有趣的事情。
例如，让我们运行一些测试 Docker 镜像：
docker run -p 888:888 -it ubuntu:16 /bin/bash
之后，准备并安装一个"简单的服务器来监听我们的端口"：
apt-get update
apt-get install -y netcat
nc -l 888
之后，我尝试从我的系统上运行 telnet localhost 888，但得到了 telnet: connect to address 127.0.0.1: Connection refused 的错误。对于 nodejs 镜像也是一样的。
但如果你尝试使用，例如，nginx 容器 -
docker run -p 888:888 -it nginx /bin/bash
我会成功：
$ telnet 127.0.0.1 888
Trying 127.0.0.1...
Connected to localhost.
这是如何可能的，我漏掉了什么？为什么我可以在 nginx 中绑定和使用任何端口，但在其他镜像中不行？
英文:
Trying investigate my issue with docker container. I lost a day when I thought that issue is in nodejs code (it has server and I am trying to connect to this server).
After investigations I found interesting thing for me.
For example - Lets run some test docker image:
docker run -p 888:888 -it ubuntu:16 /bin/bash
After that, prepare and install "simple server to listen our port":
apt-get update
apt-get install -y netcat
nc -l 888
After that I going to try to telnet localhost 888 from my system and got telnet: connect to address 127.0.0.1: Connection refused. The same with nodejs image.
But if you try to use, for example, nginx container -
docker run -p 888:888 -it nginx /bin/bash
I will be successfull:
$telnet 127.0.0.1 888
Trying 127.0.0.1...
Connected to localhost.
How it is possible, what I am missing? Why I can bind and use any port in nginx but not for other images?
答案1
得分: 0
当你运行 nc -l 888 时，你创建了一个监听 IPv4 连接的端口。如果我们运行 ss -tln，我们会看到：
State Recv-Q Send-Q 本地地址:端口 对端地址:端口 进程
LISTEN 0 1 0.0.0.0:888 0.0.0.0:*
当你在主机上运行 telnet localhost 888 时，很有可能它试图连接到IPv6的本地地址 ::1。如果你尝试连接一个仅支持IPv4的套接字，连接将失败。
如果你明确使用IPv4环回地址，可以输入 telnet 127.0.0.1 888，它应该按预期工作。
如果你通过添加 -6 参数启用了 nc 中的IPv6支持：
nc -6 -l 8888
那么你将得到一个同时监听IPv4和IPv6连接的套接字：
State Recv-Q Send-Q 本地地址:端口 对端地址:端口 进程
LISTEN 0 1 *:888 *:*
如果你尝试使用 telnet localhost 888 连接到这个套接字，它将按预期工作（telnet 127.0.0.1 888 也将正常工作）。
大多数程序（如 nginx）默认情况下会打开多协议套接字，因此这通常不是一个问题。
英文:
When you run nc -l 888, you are creating a port that is listening explicitly for IPv4 connections. If we run ss -tln, we will see:
State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
LISTEN 0 1 0.0.0.0:888 0.0.0.0:*
When you run telnet localhost 888 on your host, there's a good chance it's trying to connect to the IPv6 localhost address, ::1. This connection fails if you're trying to connect an IPv4-only socket.
If you explicitly use the IPv4 loopback address by typing telnet 127.0.0.1 888, it should work as expected.
If you enable IPv6 support in nc by adding the -6 parameter:
nc -6 -l 8888
Then you get a socket that listen for both IPv4 and IPv6 connections:
State Recv-Q Send-Q Local Address:Port Peer Address:Port Process
LISTEN 0 1 *:888 *:*
And if you attempt to connect to this socket using telnet localhost 888, it will work as expected (as will telnet 127.0.0.1 888).
Most programs (like nginx) open multi-protocol sockets by default, so this isn't normally an issue.
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