Troubleshooting “curl 52 Empty Reply From Server” with Elasticsearch and Kibana

Encountering errors when setting up your Elasticsearch and Kibana stack can be frustrating. One common issue is the “Curl 52 Empty Reply From Server” error when trying to check the health of your Elasticsearch cluster. This error, often seen alongside a “Kibana server is not ready yet” message in Kibana, indicates a problem with the connection between your client (in this case, curl and Kibana) and the Elasticsearch server.

This article will guide you through troubleshooting the “curl 52 empty reply from server” error in the context of Elasticsearch and Kibana, helping you restore communication and get your services running smoothly.

Understanding “curl 52 Empty Reply From Server”

The “curl 52 empty reply from server” error signifies that curl successfully connected to the server but received no response body. In the context of Elasticsearch, this usually means that curl connected to port 9200 (the default Elasticsearch port) but Elasticsearch didn’t send back any data.

Several factors can lead to this empty reply:

• Elasticsearch Not Listening on the Correct Host/Port: Elasticsearch might be configured to listen on a different IP address or port than you are trying to connect to with curl.
• Firewall Issues: A firewall might be blocking traffic to port 9200, preventing Elasticsearch from responding.
• Elasticsearch Service Down or Not Fully Started: Although services might appear “up,” Elasticsearch itself could be in a failed state or still initializing.
• Configuration Problems: Incorrect settings in elasticsearch.yml can prevent Elasticsearch from functioning correctly.
• Resource Exhaustion: In rare cases, server overload can lead to Elasticsearch failing to respond to requests.

Troubleshooting Steps for Elasticsearch and Kibana

Here’s a systematic approach to diagnose and resolve the “curl 52 empty reply from server” error when working with Elasticsearch and Kibana:

1. Verify Elasticsearch is Listening:

   First, confirm that Elasticsearch is indeed listening on the expected port (default 9200) and IP address. Use the lsof command as in the original example to check listening ports:

   lsof -i -P -n | grep LISTEN | grep java

   This command filters the output to show processes listening (LISTEN) on network ports and specifically looks for Java processes (as Elasticsearch is Java-based). Ensure that you see Elasticsearch listening on port 9200, usually on *:9200 or 0.0.0.0:9200 (listening on all interfaces).

   Alt text: Terminal output of lsof command showing Elasticsearch listening on port 9200

2. Check Elasticsearch Configuration (elasticsearch.yml):

   Examine your elasticsearch.yml configuration file. Key settings to review include:

   • network.host: This setting dictates the IP address Elasticsearch binds to. If it’s set to a specific IP, ensure you are trying to access Elasticsearch via that IP. Setting it to 0.0.0.0 makes Elasticsearch listen on all available interfaces.
   • http.port: Verify that this is set to 9200 (or your intended port).

   If you made changes to elasticsearch.yml, remember to restart the Elasticsearch service for the changes to take effect.

3. Examine Elasticsearch Logs:

   The Elasticsearch logs are crucial for identifying errors. Check the logs located in the directory configured by path.logs in elasticsearch.yml (default is often /var/log/elasticsearch). Look for any error messages or warnings that occurred around the time you encountered the “curl 52” error.

   In the original example, the user mentioned checking logs but finding nothing obvious. However, careful review for any exceptions or startup issues is essential.

4. Firewall Check:

   A firewall on the Elasticsearch server or any network firewall in between could be blocking connections to port 9200. Temporarily disable the firewall (if possible and safe in your environment) to test if it’s the cause. If disabling the firewall resolves the issue, you’ll need to configure it to allow traffic on port 9200 for your client IP addresses.

5. Elasticsearch Service Status:

   Use systemctl (or your system’s service management tool) to check the actual status of the Elasticsearch service:

   sudo systemctl status elasticsearch

   Even if the service shows as “active,” look for any recent restarts or errors in the status output that might indicate underlying problems.

6. Kibana Configuration (kibana.yml):

   Since you also mentioned “Kibana server is not ready yet,” verify Kibana’s configuration in kibana.yml. Specifically, check the elasticsearch.hosts setting. This should point to the correct URL(s) of your Elasticsearch instance(s). Ensure the protocol (http/https), IP address/hostname, and port are accurate.

   In the original example, Kibana logs showed connection errors (“connect ECONNREFUSED,” “write EPROTO”), suggesting a network connectivity problem or misconfiguration between Kibana and Elasticsearch, even after disabling security.

7. Network Connectivity:

   Use ping and telnet or nc (netcat) to test basic network connectivity between the machine running curl/Kibana and the Elasticsearch server.

   ping <elasticsearch_server_ip_or_hostname>
   telnet <elasticsearch_server_ip_or_hostname> 9200
   nc -vz <elasticsearch_server_ip_or_hostname> 9200

   These commands help determine if the Elasticsearch server is reachable on the network and if port 9200 is open.

Security Settings (xpack.security.enabled)

The original user tried disabling xpack.security.enabled: false in elasticsearch.yml. While this might seem relevant, the “curl 52 empty reply” error is typically a lower-level connectivity issue than authentication. Disabling security might be necessary in some setups, but it’s crucial to first ensure basic network communication and Elasticsearch service functionality are working correctly.

If you disable security, make sure both Elasticsearch and Kibana configurations are consistent with this change (e.g., Kibana should not be trying to connect using HTTPS if security is disabled in Elasticsearch and HTTPS is not configured otherwise).

Conclusion

The “curl 52 empty reply from server” error in Elasticsearch and Kibana environments often points to network connectivity problems, misconfigurations, or issues with the Elasticsearch service itself. By systematically checking configurations, logs, service statuses, and network connectivity using the steps outlined above, you can effectively diagnose and resolve the issue, bringing your Elasticsearch and Kibana stack back online. Remember to review logs thoroughly, as they usually contain valuable clues to the root cause of the problem.