private void updateSources(Request req) {
        dispatchRpcRequest(req, () -> {
            String sources = req.parameters().get(0).asString();
            String ret;
            System.out.println(proxyServer.getMode());
            if (proxyServer.getMode().requiresConfigSource()) {
                proxyServer.updateSourceConnections(List.of(sources.split(",")));
                ret = "Updated config sources to: " + sources;
            } else {
                ret = "Cannot update sources when in '" + proxyServer.getMode().name() + "' mode";
            }
            req.returnValues().add(new StringValue(ret));
            req.returnRequest();
        });
    }
Returns 0 if server is alive.

@param req a Request
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/ConfigProxyRpcServer.java