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Always randomize MAC address (#251)

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* Always randomize MAC address

* Worker: check DHCP lease time and print a warning if it's unconfigured

* Further improve the explanation

* Add two leases example to the explanation

* Add an example of the resulting /var/db/dhcpd_leases
This commit is contained in:
Nikolay Edigaryev
2025-02-13 12:35:12 +00:00
committed by GitHub
parent 2aae818f78
commit 2c8d36ef70
3 changed files with 121 additions and 8 deletions
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internal/worker/vmmanager/vm.go
+60 -8
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@@ -225,15 +225,67 @@ func (vm *VM) cloneAndConfigure(ctx context.Context) error {
}
}
// Randomize the VM's MAC-address when using bridged networking
// to avoid collisions when cloning from an OCI image on multiple hosts
// Randomize VM's MAC-address, this is important when using shared (NAT) networking
// with full /var/db/dhcpd_leases file (e.g. 256 entries) having an expired entry
// for a MAC address used by some OCI image, for example:
//
// See https://github.com/cirruslabs/orchard/issues/181 for more details.
if vm.Resource.NetBridged != "" {
_, _, err = tart.Tart(ctx, vm.logger, "set", "--random-mac", vm.id())
if err != nil {
return err
}
// {
// name=adminsVlMachine
// ip_address=192.168.64.2
// hw_address=1,11:11:11:11:11:11
// identifier=1,11:11:11:11:11:11
// lease=0x1234
//}
//
// The next VM to start with a MAC address 22:22:22:22:22:22 will assume that
// 192.168.64.2 is free (because its lease expired a long time ago) and will
// add a new entry using its MAC address and 192.168.64.2 to the
// /var/db/dhcpd_leases and won't delete the old entry:
//
// {
// name=adminsVlMachine
// ip_address=192.168.64.2
// hw_address=1,11:11:11:11:11:11
// identifier=1,11:11:11:11:11:11
// lease=0x1234
// }
// {
// name=adminsVlMachine
// ip_address=192.168.64.2
// hw_address=1,22:22:22:22:22:22
// identifier=1,22:22:22:22:22:22
// lease=0x67ade532
// }
//
// Afterward, when an OCI VM with MAC address 11:11:11:11:11:11 is cloned and run,
// it will re-use the 192.168.64.2 entry instead of creating a new one, even through
// its lease had already expired. The resulting /var/db/dhcpd_leases will look like this:
//
// {
// name=adminsVlMachine
// ip_address=192.168.64.2
// hw_address=1,11:11:11:11:11:11
// identifier=1,11:11:11:11:11:11
// lease=0x67ade5c6
// }
// {
// name=adminsVlMachine
// ip_address=192.168.64.2
// hw_address=1,22:22:22:22:22:22
// identifier=1,22:22:22:22:22:22
// lease=0x67ade532
// }
//
// As a result, you will see two VMs with different MAC address using an identical
// IP address 192.168.64.2.
//
// Another scenarion when this is important is when using bridged networking
// to avoid collisions when cloning from an OCI image on multiple hosts[1].
//
// [1]: https://github.com/cirruslabs/orchard/issues/181
_, _, err = tart.Tart(ctx, vm.logger, "set", "--random-mac", vm.id())
if err != nil {
return err
}
if vm.Resource.RandomSerial {