io.atomix.protocols.raft

Enum RaftServer.Role

java.lang.Object

java.lang.Enum<RaftServer.Role>

io.atomix.protocols.raft.RaftServer.Role

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable<RaftServer.Role>

Enclosing interface:

RaftServer

public static enum RaftServer.Role
extends java.lang.Enum<RaftServer.Role>

Raft server state types.

States represent the context of the server's internal state machine. Throughout the lifetime of a server, the server will periodically transition between states based on requests, responses, and timeouts.

Author:

Jordan Halterman

Enum Constant Summary

Enum Constants

Enum Constant and Description
CANDIDATE Represents the state of a server attempting to become the leader.
FOLLOWER Represents the state of a server participating in normal log replication.
INACTIVE Represents the state of an inactive server.
LEADER Represents the state of a server which is actively coordinating and replicating logs with other servers.
PASSIVE Represents the state of a server in the process of catching up its log.
PROMOTABLE Represents the state of a server in the process of being promoted to an active voting member.

Method Summary

Modifier and Type	Method and Description
boolean	active() Returns whether the role is a voting Raft member role.
static RaftServer.Role	valueOf(java.lang.String name) Returns the enum constant of this type with the specified name.
static RaftServer.Role[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

INACTIVE

public static final RaftServer.Role INACTIVE

Represents the state of an inactive server.

All servers start in this state and return to this state when stopped.

PASSIVE

public static final RaftServer.Role PASSIVE

Represents the state of a server in the process of catching up its log.

Upon successfully joining an existing cluster, the server will transition to the passive state and remain there until the leader determines that the server has caught up enough to be promoted to a full member.

PROMOTABLE

public static final RaftServer.Role PROMOTABLE

Represents the state of a server in the process of being promoted to an active voting member.

FOLLOWER

public static final RaftServer.Role FOLLOWER

Represents the state of a server participating in normal log replication.

The follower state is a standard Raft state in which the server receives replicated log entries from the leader.

CANDIDATE

public static final RaftServer.Role CANDIDATE

Represents the state of a server attempting to become the leader.

When a server in the follower state fails to receive communication from a valid leader for some time period, the follower will transition to the candidate state. During this period, the candidate requests votes from each of the other servers in the cluster. If the candidate wins the election by receiving votes from a majority of the cluster, it will transition to the leader state.

LEADER

public static final RaftServer.Role LEADER

Represents the state of a server which is actively coordinating and replicating logs with other servers.

Leaders are responsible for handling and replicating writes from clients. Note that more than one leader can exist at any given time, but Raft guarantees that no two leaders will exist for the same RaftCluster.getTerm().

Method Detail

values

public static RaftServer.Role[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (RaftServer.Role c : RaftServer.Role.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static RaftServer.Role valueOf(java.lang.String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

java.lang.IllegalArgumentException - if this enum type has no constant with the specified name

java.lang.NullPointerException - if the argument is null

active

public boolean active()

Returns whether the role is a voting Raft member role.

Returns:

whether the role is a voting member