alibaba/nacos · critical · ConnectException

no available server, currentServerAddr : {currentServerAddr}

Error message

no available server, currentServerAddr : {currentServerAddr}

What it means

Thrown by ServerHttpAgent.httpPost when the time window (readTimeoutMs) expires before a successful POST and before retry exhaustion. The loop condition currentTimeMillis() <= endTime became false while still iterating servers. The message includes currentServerAddr to show which node was last attempted.

Source

Thrown at client/src/main/java/com/alibaba/nacos/client/config/http/ServerHttpAgent.java:179

                    ex);
                throw ex;
            }
            
            if (serverListMgr.getIterator().hasNext()) {
                currentServerAddr = serverListMgr.getIterator().next();
            } else {
                maxRetry--;
                if (maxRetry < 0) {
                    throw new ConnectException(
                        "[NACOS HTTP-POST] The maximum number of tolerable server reconnection errors has been reached");
                }
                serverListMgr.refreshCurrentServerAddr();
            }
            
        } while (System.currentTimeMillis() <= endTime);
        
        LOGGER.error("no available server, currentServerAddr : {}", currentServerAddr);
        throw new ConnectException("no available server, currentServerAddr : " + currentServerAddr);
    }
    
    @Override
    public HttpRestResult<String> httpDelete(String path, Map<String, String> headers,
        Map<String, String> paramValues,
        String encode, long readTimeoutMs) throws Exception {
        final long endTime = System.currentTimeMillis() + readTimeoutMs;
        String currentServerAddr = serverListMgr.getCurrentServer();
        int maxRetry = this.maxRetry;
        HttpClientConfig httpConfig = HttpClientConfig.builder()
            .setReadTimeOutMillis(Long.valueOf(readTimeoutMs).intValue())
            .setConTimeOutMillis(
                ConfigHttpClientManager.getInstance().getConnectTimeoutOrDefault(100))
            .build();
        do {
            try {
                Header newHeaders = Header.newInstance();
                if (headers != null) {

View on GitHub (pinned to 9b989acdf1)

Solutions

  1. Increase the POST readTimeoutMs for config write calls.
  2. Investigate server-side latency (GC logs, disk I/O, thread dumps) on currentServerAddr.
  3. Reduce network hops/latency between client and the cluster.
  4. If the address is stale/wrong, ensure serverListMgr has the correct, current server list.
Defensive patterns

Strategy: retry

Validate before calling

// set a generous write timeout
long writeTimeoutMs = Math.max(readTimeoutMs, 10_000);

Try / catch

try {
    configService.publishConfig(dataId, group, content);
} catch (Exception e) {
    if (e.getMessage().startsWith("no available server, currentServerAddr")) {
        log.error("write timed out against {}", e.getMessage());
    }
}

Prevention

When it happens

Trigger: POST attempts each take long enough (slow TLS handshakes, read timeouts) that the cumulative wall-clock exceeds endTime; the deadline elapses mid-retry.

Common situations: Short write timeout, high-latency network, or a server that accepts connections but responds very slowly (e.g. GC stall, disk contention on the server).

Related errors

AI-assisted analysis of alibaba/nacos@9b989acdf1 (2026-08-14). Data as JSON: /api/errors/f963793b1306f17b. Report an issue: GitHub.