Leader Configuration

Overview

The leader block is where you specify configurations related to leadership election of your AtlasDB clients. It’s good practice to always specify a leader configuration, even if there is a single AtlasDB client in your cluster. If no leader configuration is specified, then AtlasDB clients will create an embedded timestamp and lock service.

Warning

If you wish to run more than one AtlasDB client with Cassandra KVS, then you must provide a leader block. Failure to do so can lead to data corruption.

Leader

Required parameters:

Property	Description
quorumSize	Number of AtlasDB clients in your cluster that form a majority. This number must be greater than half of the total number of clients.
leaders	A list of all hosts. The protocol must be http/https depending on if ssl is configured.
localServer	The protocol://hostname:port eg: https://myhost:3828 of the host on which this config exists.

Optional parameters:

Property	Description
sslConfiguration	The security settings to apply to client-side connections to the AtlasDB services at the endpoints, other than localServer, listed in the leaders array, specified according to the palantir/http-remoting library. (defaults to not using SSL)
learnerLogDir	Path to the paxos learner logs (defaults to var/data/paxos/learner)
acceptorLogDir	Path to the paxos acceptor logs (defaults to var/data/paxos/acceptor)
lockCreator	The host responsible for creation of the schema mutation lock table. If specified, this must be same across all hosts. This defaults to the first host in the sorted leaders list, so it should be consistent across nodes if not specifed.
pingRateMs	Defaults to 5000.
randomWaitBeforeProposingLeadershipMs	Defaults to 1000.
leaderPingResponseWaitMs	Defaults to 5000.

Leader Configuration Examples

Some example leader block configurations are listed below. The use of cluster and nodes are in reference to AtlasDB clients and are unrelated to your keyValueService config block.

Multiple AtlasDB Clients

A leader configuration block is required if you are using multiple AtlasDB clients. Failure to specify a leader configuration could lead to data corruption.

atlasdb:
  keyValueService:
    type: cassandra
    # omitted for brevity

  leader:
    # This should be at least half the number of nodes in your cluster
    quorumSize: 2
    learnerLogDir: var/data/paxosLogs
    acceptorLogDir: var/data/paxosLogs
    # This should be different for every node. If ssl is not enabled, then the host must be specified as http
    localServer: https://host1:3828
    # This should be the same for every node. If ssl is not enabled, then the host must be specified as http
    lockCreator: https://host1:3828
    # This should be the same for every node
    leaders:
      - https://host1:3828 # If ssl is not enabled, then the hosts must be specified as http
      - https://host2:3828
      - https://host3:3828
    sslConfiguration:
      trustStorePath: var/security/truststore.jks

Single AtlasDB Client or Offline CLI with Leader Block

Similar to the above configuration, but with only a single leader specified in leaders. To run an offline CLI, you also need to specify a leader block.

atlasdb:
  keyValueService:
    type: cassandra
    # omitted for brevity

  leader:
    # This should be at least half the number of nodes in your cluster
    quorumSize: 1
    learnerLogDir: var/data/paxosLogs
    acceptorLogDir: var/data/paxosLogs
    # This should be different for every node. If ssl is not enabled, then the host must be specified as http
    localServer: https://host1:3828
    # This should be the same for every node. If ssl is not enabled, then the host must be specified as http
    lockCreator: https://host1:3828
    # This should be the same for every node
    leaders:
      - https://host1:3828 # If ssl is not enabled, then the hosts must be specified as http

Single AtlasDB Client without Leader Block (DEPRECATED)

If you only have one AtlasDB client, then you may run with no leader block, although this option is deprecated, and will be removed in a future release. An example configuration is below.

atlasdb:
  keyValueService:
    type: cassandra
    # omitted for brevity

  # no leader block

No leader (Online CLI Only)

When you are running a client that can’t be a leader, for instance an online CLI, it is necessary to specify a remote lock and timestamp service running on your AtlasDB clients. If you are running multiple AtlasDB clients, ensure your CLI is pointing at the correct hosts and ports for the service you wish to interact with. If you are running an offline CLI then you must specify a leader block as noted above in the Single AtlasDB Client with Leader Block section.

atlasdb:
  keyValueService:
    type: cassandra
    # omitted for brevity

  # no leader block

  lock:
    servers:
      - "http://host1:3828/api"
      - "http://host2:3828/api"
      - "http://host3:3828/api"
    sslConfiguration:
      trustStorePath: var/security/truststore.jks

  timestamp:
    servers:
      - "http://host1:3828/api"
      - "http://host2:3828/api"
      - "http://host3:3828/api"
    sslConfiguration:
      trustStorePath: var/security/truststore.jks