alibaba/nacos · error · NacosException

400

400

Error message

no server available

What it means

Thrown by AiHttpClientProxy.reqApiStringWithHeader() with code INVALID_PARAM (400) when the server list is empty. This variant is used by queryAgentSpec() which fetches AgentSpec JSON with response headers (X-Nacos-AgentSpec-Md5, X-Nacos-AgentSpec-Resolved-Version). No network request is attempted — pre-flight failure.

Source

Thrown at client/src/main/java/com/alibaba/nacos/client/ai/remote/AiHttpClientProxy.java:770

        }
    }
    
    private String buildUrl(String serverAddr, String relativePath) {
        if (!serverAddr.startsWith(HTTP_PREFIX) && !serverAddr.startsWith(HTTPS_PREFIX)) {
            serverAddr = (ENABLE_HTTPS ? HTTPS_PREFIX : HTTP_PREFIX) + serverAddr;
        }
        String contextPath = serverListManager.getContextPath();
        return serverAddr + ContextPathUtil.normalizeContextPath(contextPath) + relativePath;
    }
    
    /**
     * Request API returning String body with headers exposed, propagating 304 immediately.
     */
    private HttpRestResult<String> reqApiStringWithHeader(String api,
        Map<String, String> params, RequestResource resource) throws NacosException {
        List<String> servers = serverListManager.getServerList();
        if (servers.isEmpty()) {
            throw new NacosException(NacosException.INVALID_PARAM, "no server available");
        }
        
        NacosException exception = new NacosException();
        int index = ThreadLocalRandom.current().nextInt(servers.size());
        
        for (int i = 0; i < Math.max(servers.size(), MAX_RETRY); i++) {
            String server = servers.get(index % servers.size());
            try {
                return callServerStringWithHeader(api, params, server, resource);
            } catch (NacosException e) {
                if (NacosException.NOT_MODIFIED == e.getErrCode()) {
                    throw e;
                }
                exception = e;
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("Request {} to server {} failed.", api, server, e);
                }
            }

View on GitHub (pinned to 9b989acdf1)

Solutions

1. Set serverAddr in properties before creating the AI service.
2. Verify at least one Nacos server node is reachable.
3. Check ServerListManager logs for server-list population failures.

Example fix

// before
Properties props = new Properties();
props.setProperty("namespace", "dev");
// forgot serverAddr
NacosAiFactory.createAiService(props).queryAgentSpec("spec", null, null, null);

// after
props.setProperty(PropertyKeyConst.SERVER_ADDR, "nacos.example.com:8848");
NacosAiFactory.createAiService(props).queryAgentSpec("spec", null, null, null);

if (StringUtils.isBlank(properties.getProperty(PropertyKeyConst.SERVER_ADDR))) {
    throw new IllegalStateException("serverAddr must be configured");
}
NacosAiFactory.createAiService(properties).queryAgentSpec(name, ver, label, md5);

try {
    aiService.queryAgentSpec(name, ver, label, md5);
} catch (NacosException e) {
    if (e.getErrCode() == NacosException.INVALID_PARAM && "no server available".equals(e.getErrMsg())) {
        log.error("No Nacos server configured");
    }
}

When it happens

Trigger: Calling queryAgentSpec() when serverListManager.getServerList() returns an empty list. Same root cause as errors 621/623.

Common situations: Missing serverAddr in client properties. Server list initialization failed. Client started before any server was available.

Related errors

• {exception.getErrCode()}
• NOT_MODIFIED
• 304
• {restResult.getCode()}
• INVALID_PARAM

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/2832c724a6c3c64d. Report an issue: GitHub.