https://github.com/hiteshjasani/nim-mungehosts
Programmatically alter /etc/hosts file using the command line with Docker containers
https://github.com/hiteshjasani/nim-mungehosts
docker-container dockerfile hostname nim
Last synced: 16 days ago
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Programmatically alter /etc/hosts file using the command line with Docker containers
- Host: GitHub
- URL: https://github.com/hiteshjasani/nim-mungehosts
- Owner: hiteshjasani
- License: mit
- Created: 2014-11-16T22:04:28.000Z (over 10 years ago)
- Default Branch: master
- Last Pushed: 2014-11-18T00:50:08.000Z (over 10 years ago)
- Last Synced: 2025-04-14T02:06:33.103Z (16 days ago)
- Topics: docker-container, dockerfile, hostname, nim
- Language: Nimrod
- Homepage:
- Size: 199 KB
- Stars: 50
- Watchers: 2
- Forks: 5
- Open Issues: 1
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
mungehosts
==========
Mungehosts is a tool to enable programmatically altering the `/etc/hosts` file
from the Linux command line. Run with arguments, the tool can add aliases
for localhost and add new hostname-to-ip mappings. This means you can embed
hosts file changes into your scripts -- altering the hosts file on machine
startup is a good example.
The reason this was created was due to Docker not providing any way to do this
using the Dockerfile syntax. I was building a Dockerfile that had a multi-process
server inside of it. One process expected to be able to communicate to
another process, whose hostname it received from Zookeeper. However, the hosts
file did not have a mapping for that other hostname. To make it work,
required aliasing localhost to this other hostname.
## Usage with Docker
### 1. Add the tool to your image in your Dockerfile
```
ADD https://github.com/hiteshjasani/nim-mungehosts/releases/download/v0.1.1/mungehosts /usr/local/bin/mungehosts
RUN chmod 755 /usr/local/bin/mungehosts
```
### 2. Run a startup script when running your container
When you run your container, run a startup script that invokes
mungehosts and updates your hosts file before running your server process.
See the section below on command line usage for examples.
## Command line usage
Grab the Linux binary from releases. It's an executable with no additional
dependencies than the normal C runtime so it'll work on any Linux platform.
### Aliasing localhost
To alias the hostname `foo` to `localhost`.
```bash
% sudo mungehosts -l foo
```
Will result in
```bash
127.0.0.1 localhost foo
::1 localhost foo
```
Any existing aliases will be preserved, so running the command again
with trying to alias `bar` will result in
```bash
% sudo mungehosts -l bar
% cat /etc/hosts
127.0.0.1 localhost foo bar
::1 localhost foo bar
```
### Add host mapping
To add a mapping for host `baz` at `192.168.0.1`
```bash
% sudo mungehosts -a "192.168.0.1 baz"
% cat /etc/hosts
127.0.0.1 localhost
::1 localhost
192.168.0.1 baz
```
### Help
```bash
% mungehosts --help
```
## Dependencies
### Runtime
There are no runtime dependencies other than standard C.
```bash
% ldd ./mungehosts
linux-vdso.so.1 => (0x00007fffbc9fd000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7991f40000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7991b7a000)
/lib64/ld-linux-x86-64.so.2 (0x00007f7992149000)
```
### Platforms
* Linux -- Full support, binary available in releases
* Other Unix -- Possibly works, you'll need to build the tool from source
* Windows -- no support
Basically the tool will work on any Unix platform with a `/etc/hosts` file.
There is a Linux binary in the releases, which I recommend using.
Building the tool from source is not recommended unless you have a high
pain tolerance and capacity for delayed gratification. For those who still
want to do it, step 1 is installing a Nim compiler.
Sorry, there is no support for Windows.
## FAQ
#### Why can't I update /etc/hosts using the RUN command in a Dockerfile?
Unfortunately, Docker does not persist the `/etc/hosts` file between
`RUN` commands in Dockerfiles. They only persist changes you make in
a running container. Therefore, the recommended way to use this tool
is to have a startup script that runs when starting your Docker
container. Inside this script, add lines running this tool before
starting your server process.
#### Why can't I simply use `sed` to modify `/etc/hosts`?
`sed` and similar tools actually write their changes to another temp
file and then attempt to move it over to `/etc/hosts`. The problem with
this is that some process already has the file open and the move command
fails with a message similar to
```bash
sed: cannot rename /etc/sedl8ySxL: Device or resource busy
```
Mungehosts was written to bypass this problem.
#### Do I have to install Nim?
No. Not if you use the precompiled Linux binary.
#### I'm getting a too many redirects error on OSX, help?
If you see this kind of message:
```bash
Step 4 : ADD https://github.com/hiteshjasani/nim-mungehosts/releases/download/v0.1.0/mungehosts /usr/local/src/mungehosts
2014/11/16 18:36:22 Get https://s3.amazonaws.com/github-cloud/releases/26729671/1047aa0e-6dbf-11e4-93b9-7a358f6958f9?response-content-disposition=attachment%3B%20filename%3Dmungehosts&response-content-type=application/octet-stream&AWSAccessKeyId=AKIAISTNZFOVBIJMK3TQ&Expires=1416181042&Signature=%2F1DgDIn3E9zNQvIg9QMkAWh0SZM%3D:
dial tcp: lookup s3.amazonaws.com on [10.0.2.3]:53: too many redirects
```
Then the problem may be a DNS issue if you're on OSX. A workaround for this is to log into boot2docker and update the dns servers.
```bash
% boot2docker ssh
...
docker@boot2docker:~$ cat /etc/resolv.conf
nameserver 10.0.2.3
docker@boot2docker:~$ sudo vi /etc/resolv.conf
docker@boot2docker:~$ cat /etc/resolv.conf
nameserver 10.0.2.3
nameserver 8.8.8.8
```