SetServiceConstraints API does not remove tags

[Francesco Banconi]

The usual behavior of SetServiceConstraints is to remove a constraint if the corresponding field is not included in params.SetConstraints.Constraints.

The only exception is tags (defined as a *[]string), which is instead preserved.
For consistency, I'd expect tags to be unset as well.

[Mark Brown (mstevenbrown)]

The apparent net effect of this defect is seen in the following sequence:

$ juju bootstrap --constraints tags=jujusrv #tag was created so juju server goes to correct node

$ juju get-constraints
tags=jujusrv # this tag now constrains whole environment

S juju set-constraints # this usually clears all the constraints, right?

$ juju get-constraints
tags=jujusrv

....and now I cannot deploy ANYTHING.

[Samantha Jian-Pielak (samantha-jian)]

It is "juju set-constraints tags=" to clear the bootstrap constraint.