ROLE

Introduction and Use Case(s)

The ROLE command in Redis is used to provide information about the role of the instance in a replication setup. It is particularly useful for understanding whether a Redis server is operating as a master, slave, or sentinel. Typical scenarios for using this command include monitoring replication status, debugging replication issues, and ensuring high availability configurations.

Syntax

  1. ROLE

Parameter Explanations

The ROLE command does not require any parameters.

Return Values

The return structure of the ROLE command varies depending on the role of the Redis instance:

  • Master:

    1. 1) "master"
    2. 2) (integer) number_of_slaves
    3. 3) 1) "slave_ip"
    4.    2) "slave_port"
    5.    3) "slave_state"

    Example:

    1. 1) "master"
    2. 2) (integer) 2
    3. 3) 1) 1) "127.0.0.1"
    4.       2) "6379"
    5.       3) "online"
    6.    2) 1) "127.0.0.1"
    7.       2) "6380"
    8.       3) "online"

  • Slave:

    1. 1) "slave"
    2. 2) "master_ip"
    3. 3) (integer) master_port
    4. 4) "replication_state"
    5. 5) (integer) data_received_offset

    Example:

    1. 1) "slave"
    2. 2) "127.0.0.1"
    3. 3) (integer) 6379
    4. 4) "connected"
    5. 5) (integer) 12345

  • Sentinel:

    1. 1) "sentinel"
    2. 2) 1) "monitored_master_name_1"
    3.    2) "monitored_master_name_2"

    Example:

    1. 1) "sentinel"
    2. 2) 1) "mymaster"
    3.    2) "yourmaster"

Code Examples

  1. dragonfly> ROLE
  2. 1) "master"
  3. 2) (integer) 1
  4. 3) 1) 1) "127.0.0.1"
  5.       2) "6380"
  6.       3) "online"
  8. dragonfly> ROLE
  9. 1) "slave"
  10. 2) "127.0.0.1"
  11. 3) (integer) 6379
  12. 4) "connected"
  13. 5) (integer) 45678
  15. dragonfly> ROLE
  16. 1) "sentinel"
  17. 2) 1) "mymaster"
  18.      2) "anothermaster"

Best Practices

  • Regularly use the ROLE command to monitor the state of your Redis instances, especially in complex replication setups.
  • Automate checks of the ROLE output to trigger alerts for unexpected role changes or issues in replication.

Common Mistakes

  • Ignoring the ROLE output format: Ensure that scripts parsing the ROLE output correctly handle its different formats for master, slave, and sentinel roles.

FAQs

What happens if I run the ROLE command on a standalone Redis instance?

For a standalone instance with no replication configured, the ROLE command will still indicate “master” as its role.

Can the ROLE command be used to check the status of network connections between masters and slaves?

Yes, the ROLE command provides information about the connection status of slaves to the master, which can be useful for detecting network issues.