MySQL 5.7 Reference Manual
MySQL 5.7 Release Notes
Each replica must have a unique server ID, as specified by the
server_id system variable. If
you are setting up multiple replicas, each one must have a
unique server_id value that
differs from that of the source and from any of the other
replicas. If the replica's server ID is not already set, or
the current value conflicts with the value that you have
chosen for the source server or another replica, you must
change it. With the default
server_id value of 0, a
replica refuses to connect to a source.
You can change the server_id
value dynamically by issuing a statement like this:
SET GLOBAL server_id = 21;
If the default server_id
value of 0 was set previously, you must restart the server to
initialize the replica with your new nonzero server ID.
Otherwise, a server restart is not needed when you change the
server ID, unless you make other configuration changes that
require it. For example, if binary logging was disabled on the
server and you want it enabled for your replica, a server
restart is required to enable this.
If you are shutting down the replica server, you can edit the
[mysqld] section of the configuration file
to specify a unique server ID. For example:
[mysqld]
server-id=21
A replica is not required to have binary logging enabled for
replication to take place. However, binary logging on a
replica means that the replica's binary log can be used for
data backups and crash recovery. Replicas that have binary
logging enabled can also be used as part of a more complex
replication topology. If you want to enable binary logging on
a replica, use the log-bin option in the
[mysqld] section of the configuration file.
A server restart is required to start binary logging on a
server that did not previously use it.