so the startup synchronisation didn't work, causing spurious QEMU
failures ("Device 'vde' could not be initialized").
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to run the VMs of a test. Instead, you can do
$ nix-build tests -A foo.driver
$ ./result/bin/nixos-run-vms
This uses the test driver infrastructure, which is necessary in
order to set up the VDE switches.
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together into virtual networks. This has several advantages:
- It's more secure because the QEMU instances use Unix domain
sockets to talk to the switch.
- It doesn't depend on the host's network interfaces. (Local
multicast fails if there is no default gateway, so for instance it
fails if a laptop is not connected to any network.)
- VDE devices can be connected together to form arbitrary network
topologies.
- VDE has a "wirefilter" tool to emulate delays and packet loss,
which are useful for network testing.
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is now made available in the interactive test driver. For instance,
you can do
$ nix-build tests/ -A quake3.driver
$ ./result/bin/nixos-test-driver
> eval $ENV{'testScript'};
... see VMs + X11 + Quake get started, bots running around ...
>
So after this you can run commands interactively on the VMs in the
state they were in after the conclusion of the test script.
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interactively on a network specification. For instance:
$ nix-build tests/ -A quake3.driver
$ ./result/bin/nixos-test-driver
> startAll;
client1: starting vm
client1: QEMU running (pid 14971)
server: starting vm
server: QEMU running (pid 14982)
...
> $client1->execute("quake3 ...");
* Use the GNU readline library in interactive mode.
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It turns out that all network interfaces in all VMs had the same
Ethernet address (52:54:00:12:34:56) because we didn't specify any
with the macaddr=... option. This can obviously lead to great
confusion. For instance, when a router forwards a packet, it can
actually end up sending the packet to itself because the target
machine has the same Ethernet address (causing a loop until the TTL
expires), while the target *also* receives the packet. It's amazing
anything worked at all, really.
So now we just set the Ethernet addresses to 52:54:00:12:<virtual
network number>:<machine number>.
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which NixOS should be built. This is useful in NixOS network
specifications, because it allows machines in the network to have
different types, e.g.,
{
machine1 =
{ config, pkgs, ... }:
{ nixpkgs.system = "i686-linux";
... other config ...
};
machine2 =
{ config, pkgs, ... }:
{ nixpkgs.system = "x86_64-linux";
... other config ...
};
}
It can also be useful in distributed NixOS tests.
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- Added a backdoor option to the interactive run-vms script. This allows me to intergrate the virtual network approach with Disnix
- Small documentation fixes
Some explanation:
The nixos-build-vms command line tool can be used to build a virtual network of a network.nix specification.
For example, a network configuration (network.nix) could look like this:
{
test1 =
{pkgs, config, ...}:
{
services.openssh.enable = true;
...
};
test2 =
{pkgs, config, ...}:
{
services.openssh.enable = true;
services.xserver.enable = true;
}
;
}
By typing the following instruction:
$ nixos-build-vms -n network.nix
a virtual network is built, which can be started by typing:
$ ./result/bin/run-vms
It is also possible to enable a backdoor. In this case *.socket files are stored in the current directory
which can be used by the end-user to invoke remote instruction on a VM in the network through a Unix
domain socket.
For example by building the network with the following instructions:
$ nixos-build-vms -n network.nix --use-backdoor
and launching the virtual network:
$ ./result/bin/run-vms
You can find two socket files in your current directory, namely: test1.socket and test2.socket.
These Unix domain sockets can be used to remotely administer the test1 and test2 machine
in the virtual network.
For example by running:
$ socat ./test1.socket stdio
ls /root
You can retrieve the contents of the /root directory of the virtual machine with identifier test1
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guest connect to a Unix domain socket on the host rather than the
other way around. The former is a QEMU feature (guestfwd to a
socket) while the latter requires a patch (which we can now get rid
of).
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