Elasticsearch ConnectException: Connection refused - Common Causes & Fixes

Brief Explanation

The "ConnectException: Connection refused" error in Elasticsearch occurs when a client or node attempts to establish a connection with an Elasticsearch server or another node, but the connection is actively rejected by the target system.

Impact

This error can have significant impacts on Elasticsearch operations:

• Prevents clients from performing queries or indexing operations
• Disrupts cluster communication, potentially leading to split-brain scenarios
• Affects data replication and cluster health
• May cause application downtime or degraded performance

Common Causes

1. Elasticsearch service is not running on the target system
2. Firewall blocking the Elasticsearch port (default 9200)
3. Incorrect host or port configuration in the client
4. Network connectivity issues
5. Elasticsearch bound to localhost instead of the network interface

Troubleshooting and Resolution Steps

1. Verify Elasticsearch service status:

   sudo systemctl status elasticsearch
   

2. Check if Elasticsearch is listening on the correct port:

   netstat -tuln | grep 9200
   

3. Ensure firewall allows connections to Elasticsearch port:

   sudo ufw allow 9200/tcp
   

4. Verify network connectivity using tools like ping or telnet

5. Check Elasticsearch configuration (elasticsearch.yml) for correct network.host and http.port settings

6. Review client configuration for correct Elasticsearch host and port

7. Inspect Elasticsearch logs for any startup or binding errors:

   tail -f /var/log/elasticsearch/elasticsearch.log
   

8. Restart Elasticsearch service if necessary:

   sudo systemctl restart elasticsearch
   

Best Practices

• Always bind Elasticsearch to a specific IP or network interface, not just localhost
• Use proper security measures like TLS/SSL and authentication
• Implement monitoring to detect connectivity issues early
• Keep Elasticsearch and client libraries updated to the latest compatible versions

Frequently Asked Questions

Q: Can a firewall cause the "Connection refused" error?
A: Yes, a firewall blocking the Elasticsearch port (default 9200) can cause this error. Ensure your firewall rules allow traffic to and from the Elasticsearch port.

Q: How can I check if Elasticsearch is actually running?
A: You can check the Elasticsearch service status using the command sudo systemctl status elasticsearch on systems using systemd, or by checking the process list with ps aux | grep elasticsearch.

Q: What should I do if Elasticsearch is running but still getting "Connection refused"?
A: Check the elasticsearch.yml configuration file to ensure Elasticsearch is bound to the correct network interface and not just localhost. Also, verify that the client is using the correct host and port.

Q: Can network issues between nodes cause this error in a cluster?
A: Yes, network connectivity problems between Elasticsearch nodes can cause "Connection refused" errors, potentially disrupting cluster operations. Ensure all nodes can communicate with each other on both transport and HTTP ports.

Q: How do I resolve "Connection refused" errors in a Docker environment?
A: In Docker, ensure that the Elasticsearch container is exposing the correct ports and that you're using the right network settings. Check Docker network configurations and make sure you're connecting to the correct container IP or hostname.