1 问题描述
在使用cargo进行复杂软件安装时， 依赖比较多的库， 需要快速下载， 出现了该问题“Couldn't resolve host name (Could not resolve host: crates)”， 错误日志如下：
1 $ cargo install mdbook
2 Updating `git://mirrors.ustc.edu.cn/crates.io-index` index
3 Installing mdbook v0.4.4
4 Downloaded byteorder v1.3.4 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
5 Downloaded inotify-sys v0.1.4 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
6 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
7 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
8 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
9 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
10 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
11 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
12 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
13 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
14 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
15 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
16 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
17 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
18 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
19 warning: spurious network error (2 tries remaining): [6] Couldn't resolve host name (Could not resolve host: crates)
20 Downloaded input_buffer v0.3.1 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
21 。。。// 跳过部分日志
22 error: failed to compile `mdbook v0.4.4`, intermediate artifacts can be found at `/tmp/cargo-installzrH2PU`
23
24 Caused by:
25 failed to download from `https://crates-io.proxy.ustclug.org/api/v1/crates/tokio-tungstenite/0.11.0/download`
26
27 Caused by:
28 [6] Couldn't resolve host name (Could not resolve host: crates)
看到该问题， 还特意检查了网络， 设置了dns，
在文件 /etc/resolv.conf 中增加了阿里的dns域名服务器， 问题没有解决;
nameserver 223.5.5.5
nameserver 223.6.6.6
查找资料找到了问题根因和解决办法;
2 解决办法
临时规避，禁止并行化下载安装， 命令行输入： CARGO_HTTP_MULTIPLEXING=false cargo install mdbook
$ CARGO_HTTP_MULTIPLEXING=false cargo install mdbook
pdating `git://mirrors.ustc.edu.cn/crates.io-index` index
Installing mdbook v0.4.4
Downloaded cfg-if v0.1.10 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded bytes v0.5.6 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded futures-io v0.3.8 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded http-body v0.3.1 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded markup5ever_rcdom v0.1.0 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded num-integer v0.1.44 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded phf_shared v0.8.0 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded rand_pcg v0.2.1 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
Downloaded serde_urlencoded v0.6.1 (registry `git://mirrors.ustc.edu.cn/crates.io-index`)
。。。
Compiling markup5ever_rcdom v0.1.0
Compiling ammonia v3.1.0
Compiling hyper v0.13.9
Compiling warp v0.2.5
Compiling mdbook v0.4.4
Finished release [optimized] target(s) in 3m 01s
Installing /home/neo/.cargo/bin/mdbook
Installed package `mdbook v0.4.4` (executable `mdbook`)
编译时间略长， 也还可以接受。。。
3 引申阅读
问题根因分析：
详见：https://github.com/ustclug/discussions/issues/294
主要原因如下：
knight42 commented on Apr 30
我找到这个问题的原因了，是因为我们的 nginx 会根据 client ip 对请求数作限制，默认是 4r/s 即每秒 4 个请求，如果超过的话就会返回 503。而我们的 nginx 配置里有这么一段
error_page 500 502 503 504 =302 $scheme://$proxy_host$uri;
即当上游返回 503 的时候，nginx 会让 client 302 到 $scheme://$proxy_host$uri，而这个时候 nginx 还没开始做 proxy，$proxy_host 应该还是空的，
所以 client 会看到 nginx 返回的 302 的响应里的 location 是 https:///crates/futures-io/futures-io-0.3.4.crate.
目前我先对 crates-io.proxy.ustclug.org 稍微放开了一下限制
limit_req_zone $binary_remote_addr zone=rust-crates:10m rate=20r/s;
limit_req zone=rust-crates burst=150;
同时调整了一下配置，减少了一次 302 跳转，@s977120 你现在可以试试看有没有问题。
不过感觉这个只是临时的 workaround，要彻底解决应该要让 cargo 限制一下并发请求数。
最终解决方案， 要控制cargo下载时的并发数， 估计要看一下源码，确认如何实现的。当前尝试使用cargo install -j 4 时，问题依旧;
使用说明如下：
$ cargo install --help
cargo-install
Install a Rust binary. Default location is $HOME/.cargo/bin
USAGE:
cargo install [OPTIONS] [--] [crate]...
OPTIONS:
-q, --quiet No output printed to stdout
--version Specify a version to install
--git Git URL to install the specified crate from
--branch Branch to use when installing from git
--tag Tag to use when installing from git
--rev Specific commit to use when installing from git
--path Filesystem path to local crate to install
--list list all installed packages and their versions
-j, --jobs Number of parallel jobs, defaults to # of CPUs
-f, --force Force overwriting existing crates or binaries
--no-track Do not save tracking information
--features ... Space or comma separated list of features to activate
--all-features Activate all available features
--no-default-features Do not activate the `default` feature
--profile Install artifacts with the specified profile
--debug Build in debug mode instead of release mode
--bin ... Install only the specified binary
--bins Install all binaries
--example ... Install only the specified example
--examples Install all examples
--target ... Build for the target triple
--target-dir Directory for all generated artifacts
--root Directory to install packages into
--index Registry index to install from
--registry Registry to use
-v, --verbose Use verbose output (-vv very verbose/build.rs output)
--color Coloring: auto, always, never
--frozen Require Cargo.lock and cache are up to date
--locked Require Cargo.lock is up to date
--offline Run without accessing the network
-Z ... Unstable (nightly-only) flags to Cargo, see 'cargo -Z help' for details
-h, --help Prints help information
ARGS:
...
Run `cargo help install` for more detailed information.