public LoadBalancer with(State state, Instant changedAt) {
        if (changedAt.isBefore(this.changedAt)) {
            throw new IllegalArgumentException("Invalid changeAt: '" + changedAt + "' is before existing value '" +
                                               this.changedAt + "'");
        }
        if (this.state != State.reserved && state == State.reserved) {
            throw new IllegalArgumentException("Invalid state transition: " + this.state + " -> " + state);
        }
        return new LoadBalancer(id, idSeed, instance, state, changedAt);
    }
Returns a copy of this with state set to given state
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/lb/LoadBalancer.java