devns 0.4.6

Pure Python DNS server for developers

PyDevNS is a pure Python DNS server for developers. You know how you need a domain name to use for interacting with your app locally? Well, this is the tool for you.

Installation

pip install devns

Hey, not everything has to be hard.

Rationale

I know what you’re thinking:

Dude, what? I just put local.dev in my /etc/hosts file.

That’s all well and good, but what about when you need local.dev and *.local.co?

There’s like a million things out there that do this. I could use dnsmasq, or one of the other 40 random Python “dev DNS” servers you probably stole your implementation from.

OK, dnsmasq kind of seems like overkill, but what about when you need local.dev or reallycoolprogrammer.local.dev to work from inside a docker container?

Well then I just make dnsmasq resolve it to my real IP instead of 127.0.0.1.

So you edit the config and restart dnsmasq every time you move from home, to the coffee shop, to the office, wherever…

That is kind of a pain, now that you mention it…

Thought so.

Default Behavior

If you run devns with no arguments, the server will start, bind to 0.0.0.0 with a random port and try to discover a suitable IP address to use for resolving any incoming DNS requests. It literally does not care what domain you ask for, it always responds and always with the same IP, hopefully the IP address of your actual network interface (e.g. 192.168.1.52 or whatever). It tries to figure that out on its own, and I think it does a pretty good job of it.

But then how do I make DNS queries go to it, especially if it’s using a random port every time it runs?

Glad you asked. It’ll also try to write a file to /etc/resolver/dev, which if your OS supports such things, would tell it to send any DNS queries for domains ending it .dev to devns.

But wouldn’t I need to…

Run it with sudo to do that? Yeah probably, unless your system is insane and just lets anybody write to /etc all willy nilly, in which case you have bigger problems than getting local.dev to resolve to something sensible.

Don’t I have to restart it every time my IP changes, just like dnsmasq?

No, there’s a configurable TTL associated with the address devns uses in its responses. By default, that’s 5 minutes. If a query comes in and the address was last confirmed more than 5 minutes prior, it’ll try to rediscover it. That should cover most cases of relocating from one spot to another.

Examples

Run the server with a random port and auto-configured resolver for .dev resolving to a sensible, auto-detected IP address:

sudo devns

Rediscover the response address every 15 minutes instead of 5:

sudo devns --ttl 900

Listen on port 53535 without writing any resolver files:

devns --port 53535 --no-resolver

Write the resolver files to /usr/local/etc/resolver instead of /etc/resolver:

devns --resolver-dir /usr/local/etc/resolver

Respond to all queries with 172.24.3.1, and ignore the TTL:

sudo devns --address 172.24.3.1

Listen on port 53535, write config files for .dev and .local.co:

sudo devns --port 53535 --domains dev local.co

Bind to a random port on 127.0.0.1, and make a lot of noise:

sudo devns --host 127.0.0.1 -vvv

Notes/Caveats

If you have entries in your /etc/hosts for any domains you want to use with devns, you’ll have to remove those. That’s all.

Usage

Here’s what devns --help gets you:

usage: devns [-h] [--version] [--verbose | --quiet]
             [--address ADDRESS | --ttl SECONDS] [--host HOST] [--port PORT]
             [--domains [DOMAIN [DOMAIN ...]]] [--resolver-dir DIRECTORY]
             [--no-resolver]

PyDevNS - A DNS server for developers.

optional arguments:
  -h, --help            show this help message and exit
  --version             show version and exit

Logging:
  --verbose, -v         verbose output
  --quiet, -q           quiet mode

Address:
  --address ADDRESS, -a ADDRESS
                        IP address to respond with
  --ttl SECONDS, -t SECONDS
                        how often to refresh the address

Network:
  --host HOST, -H HOST  address to listen on
  --port PORT, -p PORT  port to listen on

Resolver:
  --domains [DOMAIN [DOMAIN ...]], -d [DOMAIN [DOMAIN ...]]
                        domains to create resolver files for
  --resolver-dir DIRECTORY, -rd DIRECTORY
                        where to put resolver files
  --no-resolver, -nr    disable creating resolver files