How to configure custom hostname to IP resolutions in my system for web development - development-environment

Question

Preface
A web app can potentially
serve different pages,
depending on the
hostname
that is requested by the browser,
even if all hostnames are resolved
to the same
IP address.
Example
For example, at
https://app.example.com,
which resolves to
1.2.3.4,
users will find the user interface
and at
https://admin.example.com,
which also resolves to
1.2.3.4,
awaits a dashboard
through which
only the app's owner can
administrate users and data
in the app.
What We Need
In short,
we need to enter,
for example,
http://admin.app:8000/
in our browsers
and have that admin.app resolve to 127.0.0.1.
The Question
How can I configure
custom hostname to IP address resolutions
in my development environment?

Answer 1

(Ubuntu and Derivatives) Configure NetworkManager's dnsmasq
Ubuntu Desktop's default networking configuration is
composed of NetworkManager and its slave dnsmasq.
The slave dnsmasq listens at 127.0.1.1 and /etc/resolv.conf lists it as the only nameserver.
This has
some benefits.
What it means for this purpose is that we have a fully configurable DNS server, comfortably configured by default.
We can create
/etc/NetworkManager/dnsmasq.d/hosts.conf
and put in it whatever address statements we'd like:
address=/admin.app/127.0.0.1
We can even use wildcards!
address=/.app/127.0.0.1
See the
dnsmasq documentation
for details
(look for --address).
Since dnsmasq is started by the network-manager service,
then I would assume that the following would restart it
so that new configuration would take effect:
$ service network-manager restart
But its init-script does not control slave dnsmasq.
Therefore the dnsmasq process must be killed and then
the above command would have it start again.
And that is it!

Answer 2

(Linux) User Specific HOSTALIASES File
Very limited
This would have been my preferred answer
because
it refrains from
altering system configuration.
But:
It does not support wildcards
It does not support hostname to IP address resolution
It does not support freely configurable subdomains
It will not work if you have a local DNS server,
which is the case in modern Ubuntu.
What is It
It is a user specific host aliases file.
Notice that the format is not the same as the hosts file.
In short, you create a file
which contains host aliases.
For example
foo localhost
bar localhost
and place it at ~/.hosts.
Then you set an environment variable
HOSTALIASES
with the path to the aliases file.
So, for this example
$ export HOSTALIASES=~/.hosts

Answer 3

If Testing In a Virtual Machine
In a virtual machine
127.0.0.1 and localhost
will not reach the host,
but the guest.
In VirtualBox, for example,
by default, the host can be reached
at 10.0.2.2.
So, the guest VM's hosts file can look like
10.0.2.2 host
10.0.2.2 app.host
10.0.2.2 admin.host
Proxy DNS Nameserver Inside a Virtual Machine
If you're setting up
a proxy DNS nameserver
inside a virtual machine
(perhaps for wildcard support in Windows)
the upstream nameserver
is usually provided by the host.
In VirtualBox, it is 10.0.2.3.

Answer 4

(Windows) Configuring Acrylic DNS Server
Acrylic DNS Proxy is easy to install and configure.
It can help us get hostnames with aliases quickly in Windows.
And it is open source.
Install it.
Open the hosts file (via the start menu entry).
Put in some entries, like 1.2.3.4 >app.
Clear its cache and restart it (via the start menu entry).
Set your DNS server to 127.0.0.1.

Answer 5

(Windows, Linux, OSX) System Wide Hosts File
Simply edit the
hosts file.
Its location
depends on the OS.
For example:
127.0.0.1 app.localhost
127.0.0.1 admin.localhost
On Windows you can use
this nifty open source GUI
for editing the hosts file:
Hosts File Editor.
Wildcards
The hosts file does not support wildcards!
Ubuntu Desktop
Since Ubuntu 12.04,
Ubuntu desktop comes with
a local DNS server,
which might not respect
the hosts file (/etc/hosts).
So, for Ubuntu desktop, this answer
is best.

Answer 6

(GNU/Linux)
Since all the major distributions are migrating (or already did) to systemd stack the proper place to implement wildcard support would be systemd-resolved: see https://github.com/systemd/systemd/issues/766 for details.
That would be the place to set custom overrides for DNS as well.
As for windows - its VM should just get DNS from host machine: it's to risky to run it on bare metal anyway.