Minimal Docker for Networking Rust Binary

user_2547570 0
Viewed 342

I have a Rust binary I want to put in a docker image. To minimize the image size, I used http://github.com/larsks/dockerize/ which adds libc and a few nss library files. However it's failing to resolve DNS and I want to know what's the hidden system file dependency of reqwest or hyper.

Here is an example:

Cargo.toml

[package]                                                                                                                                                                                                                                  
name = "example"    
version = "0.1.0"    
edition = "2018"    
    
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html    
    
[dependencies]    
reqwest = { version = "0.11.4", default-features = false, features = ["json", "rustls-tls"] }    
tokio = { version = "1.8.1", features = [ "full" ] }

src/main.rs

#[tokio::main]                                                                                                                                                                                                                            
async fn main() {    
    println!("{:?}", reqwest::get("https://bing.com").await);
}

Building the image with certs and strace:

❯ dockerize --tag test --add-file /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt --add-file /usr/bin/strace /usr/bin/strace --add-file $(pwd)/target/debug/example /app/example

Successfully tagged test:latest

The resulting docker image:

│ Current Layer Contents ├───────────────────────────────────────────────────────────────────────────────────────────
Permission     UID:GID       Size  Filetree
-rw-r--r--         0:0       25 B  ├── Dockerfile
drwxr-xr-x         0:0      60 MB  ├── app
-rwxr-xr-x         0:0      60 MB  │   └── example
drwxr-xr-x         0:0     203 kB  ├── etc
-rw-r--r--         0:0      126 B  │   ├── group
-rw-r--r--         0:0       76 B  │   ├── nsswitch.conf
-rw-r--r--         0:0      513 B  │   ├── passwd
drwxr-xr-x         0:0     202 kB  │   └── ssl
drwxr-xr-x         0:0     202 kB  │       └── certs
-r--r--r--         0:0     202 kB  │           └── ca-certificates.crt
drwxr-xr-x         0:0     343 kB  ├── lib64
-rwxr-xr-x         0:0     222 kB  │   ├── ld-linux-x86-64.so.2
-rwxr-xr-x         0:0      40 kB  │   ├── libnss_compat.so.2
-rwxr-xr-x         0:0      31 kB  │   ├── libnss_dns.so.2
-rwxr-xr-x         0:0      51 kB  │   └── libnss_files.so.2
drwxr-xr-x         0:0     4.2 MB  └── usr
drwxr-xr-x         0:0     4.2 MB      └── lib
-rwxr-xr-x         0:0     2.2 MB          ├── libc.so.6
-rwxr-xr-x         0:0      23 kB          ├── libdl.so.2
-rw-r--r--         0:0     476 kB          ├── libgcc_s.so.1
-rwxr-xr-x         0:0     1.3 MB          ├── libm.so.6
-rwxr-xr-x         0:0      40 kB          ├── libnss_compat.so.2
-rwxr-xr-x         0:0      31 kB          ├── libnss_dns.so.2
-rwxr-xr-x         0:0      51 kB          ├── libnss_files.so.2
-rwxr-xr-x         0:0     154 kB          └── libpthread.so.0

Running the binary fails with "Device or resource busy" msg:

❯ docker run test /app/example
Err(reqwest::Error { kind: Request, url: Url { scheme: "https", cannot_be_a_base: false, username: "", password: None, host: Some(Domain("bing.com")), port: None, path: "/", query: None, fragment: None }, source: hyper::Error(Connect, ConnectError("dns error", Os { code: 16, kind: ResourceBusy, message: "Device or resource busy" })) })

What's confusing is that ping binary in the same environment just works. This means reqwest or hyper needs additional setting or file. I ran strace to find out what they require but couldn't find it. I also tried the trust-dns feature of reqwest and it works for only some domains.

Here is strace of the binary:

❯ docker run test strace /app/example 2>&1 | rg open
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/glibc-hwcaps/x86-64-v3/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/glibc-hwcaps/x86-64-v2/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/tls/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/x86_64/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/usr/lib/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/proc/self/maps", O_RDONLY|O_CLOEXEC) = 3
openat(AT_FDCWD, "/proc/self/cgroup", O_RDONLY|O_CLOEXEC) = 3

What should I add to the image so the reqwest+hyper with tls works?

reqwest hyper rust docker
2 Answers

Hyper by default resolves DNS by getaddrinfo().
There are users experiencing similar issues using getaddrinfo() within docker.

#include "netdb.h"                                                                                                                                                                                                                                                                                                                                       
#include "stdio.h"    
    
int main( int argc, const char* argv[] )    
{    
   const struct addrinfo* hints = 0;    
   struct addrinfo* aihead = 0;    
    
   int error = getaddrinfo( "www.google.com", "80", hints, &aihead);    
   if ( error )    
   {    
      printf( "Got error: %s\n", gai_strerror( error ) );    
      return error;    
   } else {    
      printf( "got dns ok." );    
   }    
}

The solution is to copy /usr/lib/libnss* and /usr/lib/libresolv* as well in addition to the current listing in the question.

user_25475700

An alternative solution is to configure Hyper not to use getaddrinfo and keep the address resolution entirely in rust.

You can do this in Reqwest by setting the trust_dns feature on the crate, which makes it use trust_dns_resolver instead of getaddrinfo.

user_70991480
Related