Do not startup the HTTP server by default

[codebien]

We should not startup the HTTP server for the REST API by default. It'd be better to startup it only if explicitly requested.

[janHildebrandt98]

Hi @codebien
I could work on this.

Right now we only start the http server if GlobalFlags.Address is not the empty string. It defaults to localhost:6565 which means the server is enabeld by default.

Do we want a separate flag controlling if the server should be started (something like --startRestServer) or would it suffice to just change the default of Address to ""?

[codebien]

Hey @janHildebrandt98, thanks for volunteering. The expectation is whoever will pick the task must design a proposal.

Independently from the solution adopted, I think the important part is the current command for disabling the server should generate the same behavior. Eventually, it could error but it mustn't flip the logic. It means if the user types the following command: k6 run -a '' script.js they shouldn't get a started server. If we should just keep the same logic or returning an error has to be decided, or we might have evaluate other options.

I guess there are several approaches and we should evaluate the best trade-off:

• We might decide to introduce a completely new flag and drop the old
• Keep both and make them work together
• Deprecated the old and introduce a new one
• Probably something else

[janHildebrandt98]

@codebien
I would advocate for introducing a new flag (--startRestServer?) but keep the old -a as well.
-a will be ignored when --startRestServer is not set which ensures same behavior as previously. Else it allows to change the port, just as before.
While it is a little cumbersome to have 2 different parameters, I think this way we have no magical behavior (i.e. setting -a to "" will disable the server) but its instead clear with a separate flag.

We will need to add some validation that ensures -a is not "" when --startRestServer is set etc.
What do you think?