alibaba/nacos · critical · NacosException

400

400

Error message

no server available

What it means

Thrown by NamingHttpClientProxy.reqApi when the server list is empty and the client is not in domain mode (NacosException.INVALID_PARAM = 400). The HTTP proxy has no server to send the request to. This fires before any retry logic because there is nothing to retry against.

Source

Thrown at client/src/main/java/com/alibaba/nacos/client/naming/remote/http/NamingHttpClientProxy.java:385

    /**
     * Request api.
     *
     * @param api     api
     * @param params  parameters
     * @param body    body
     * @param servers servers
     * @param method  http method
     * @return result
     * @throws NacosException nacos exception
     */
    public String reqApi(String api, Map<String, String> params, Map<String, String> body,
        List<String> servers,
        String method) throws NacosException {
        
        params.put(CommonParams.NAMESPACE_ID, getNamespaceId());
        
        if (CollectionUtils.isEmpty(servers) && !serverListManager.isDomain()) {
            throw new NacosException(NacosException.INVALID_PARAM, "no server available");
        }
        
        NacosException exception = new NacosException();
        if (serverListManager.isDomain()) {
            String nacosDomain = serverListManager.getNacosDomain();
            for (int i = 0; i < maxRetry; i++) {
                try {
                    return callServer(api, params, body, nacosDomain, method);
                } catch (NacosException e) {
                    exception = e;
                    if (NAMING_LOGGER.isDebugEnabled()) {
                        NAMING_LOGGER.debug("request {} failed.", nacosDomain, e);
                    }
                }
            }
        } else {
            int index = ThreadLocalRandom.current().nextInt(servers.size());
            

View on GitHub (pinned to 9b989acdf1)

Solutions

1. Verify the serverAddr property in the client configuration points to a reachable Nacos server.
2. Ensure the server list is populated before issuing naming requests — add a startup delay or readiness check.
3. If using a domain/VIP, confirm serverListManager.isDomain() returns true so the domain path is used instead of the server-list path.

// Ensure server list is populated before issuing naming requests
ServerListManager slm = ...; // from client internals
if (slm.getServerList().isEmpty() && !slm.isDomain()) {
    throw new IllegalStateException("No Nacos server available — check serverAddr config");
}

try {
    namingService.registerInstance(serviceName, instance);
} catch (NacosException e) {
    if (e.getErrCode() == NacosException.INVALID_PARAM
        && "no server available".equals(e.getErrMsg())) {
        // wait for server list to populate, then retry
        Thread.sleep(2000);
        namingService.registerInstance(serviceName, instance);
    } else {
        throw e;
    }
}

When it happens

Trigger: The ServerListManager has not yet retrieved any server addresses (or all were removed) and no domain/virtual-IP is configured. Any naming HTTP API call (register, query, etc.) will immediately fail.

Common situations: Startup race where the client sends a naming request before the server list has been fetched; misconfigured server address property (empty or unparseable); the Nacos server endpoint is unreachable during initial server-list discovery; the server list was cleared by a failed health-check sweep.

Related errors

• serverList is empty,please check configuration
• Do not support register ephemeral instances by HTTP, please
• Do not support persistent instances to perform batch registr
• Do not support persistent instances to perform batch de regi
• Do not support query instance by http client,please use gRPC

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/88c4bd4398eef5c4. Report an issue: GitHub.