final public List<JRTConnection> getSources() {
        List<JRTConnection> ret;
        synchronized (connections) {
            ret = new ArrayList<>(connections.values());
        }
        return ret;
    }
Preconditions:
1. the current connection is unhealthy and should not be selected when switching
2. There is more than 1 source.
config/src/main/java/com/yahoo/vespa/config/JRTConnectionPool.java