Brittle behavior when starting subsequent tsnsrv instances.

[efarrer]

When a user runs tsnsrv as follows:

TS_AUTHKEY=... tsnsrv --name first http://localhost:9090

Then everything works wonderfully.

However if I try and start a second instance.

TS_AUTHKEY=... tsnsrv --name second http://localhost:9090

Then the second instance will fail and the tailscale console will report the error: "Duplicate node key" under the Machine tab.

The conflict is caused by the tsnsrv alwasys using the .config/tsnet-tsnsrv directory (on Linux) to store configuration. This behavior can be avoided by using the -stateDir or TS_STATE_DIR for the second instance however the failure is surprising and will likely lead to confusion. A better solution would be to use a unique directory name (based on the --name parameter) for each tsnsrv instance such as .config/tsnet-tsnsrv-. This would eliminate the surprises and confusion for users.

The cost of this proposal is that it is a backwards incompatible change and that existing users would need to recreate their instances (use a new key). If desired tsnsrv could warn users of the incompatibility by warning all users that have a .config/tsnet-tsnsrv directory that they should delete this directory and recreate their instances.