YCQL connection issues

1. Are YugabyteDB processes running?

First, ensure that the expected YugabyteDB processes on the current node. At a minimum, the tserver process needs to be running to be able to connect to this node with a YCQL client or application. Additionally, depending on the setup, you might expect a master process to also be running on this node. Follow the instructions on the Check Processes page.

2. Is the Cassandra-compatible YCQL API running?

If the tserver process is running, make sure the YCQL API is enabled and listening on the YCQL port (default 9042).

$ lsof -i :9042

COMMAND     PID   USER   FD   TYPE     DEVICE SIZE/OFF NODE NAME
yb-tserve 81590 centos  131u  IPv4 0xdeadbeef      0t0  TCP localhost:9042 (LISTEN)

Note: You may need to install lsof first.

When running a local cluster with yb-ctl you should see all the nodes here with different IP addresses. For instance:

$ lsof -i :9042

COMMAND     PID   USER   FD   TYPE     DEVICE SIZE/OFF NODE NAME
yb-tserve 81590 centos  131u  IPv4 0xdeadbeef      0t0  TCP localhost:9042 (LISTEN)
yb-tserve 81593 centos  131u  IPv4 0xdeadbeef      0t0  TCP 127.0.0.2:9042 (LISTEN)
yb-tserve 81596 centos  131u  IPv4 0xdeadbeef      0t0  TCP 127.0.0.3:9042 (LISTEN)

If there is another process using this port you might need to stop that and restart the YB-TServer process. Otherwise, if no process is listening but the YB-TServer is running, check the value of the --cql_proxy_bind_address flag passed to the YB-TServer process.

3. Can ycqlsh connect locally?

Once on the machine where YugabyteDB is running, use ycqlsh to connect to the local YugabyteDB instance. Depending on your installation, you may need to install ycqlsh, otherwise you can find it in the YugabyteDB bin directory. Try running:

$ ycqlsh <yb-local-address>

where <yb-local-address> is the address where the YugabyteDB YCQL server is listening (for example, as returned by lsof). For instance, in the example above, it is localhost (or, additionally, 127.0.0.2 and 127.0.0.3 for the yb-ctl case).

If ycqlsh can connect, the issue is likely a network issue with the original client not being able to access this node where YugabyteDB is running. See also Are Master or TServer endpoints accessible?.