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.

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()}
• 304
• NOT_MODIFIED
• {restResult.getCode()}
• Can't get batched data from single data.

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

Appendix: 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);
                }
            }

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