The Ultimate Guide to High Availability with MariaDB
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Binlogrouter

Binlogrouter

The binlogrouter is a replication protocol proxy module for MariaDB MaxScale. This module allows MariaDB MaxScale to connect to a master server and retrieve binary logs while slave servers can connect to MariaDB MaxScale like they would connect to a normal master server. If the master server goes down, the slave servers can still connect to MariaDB MaxScale and read binary logs. You can switch to a new master server without the slaves noticing that the actual master server has changed. This allows for a more highly available replication setup where replication is high-priority.

Table of Contents

Configuration

Mandatory Router Parameters

The binlogrouter requires the user and password parameters. These should be configured according to the Configuration Guide.

In addition to these two parameters, the server_id and binlogdir parameters needs to be defined.

Router Parameters

The binlogrouter accepts the following parameters.

Note: Earlier versions of MaxScale supported the configuration of the binlogrouter only via router_options (a the comma-separated list of key-value pairs). As of MaxScale 2.1, all of the router options should be defined as parameters. The values defined in router_options will have priority over the parameters to support legacy configurations. The use of router_options is deprecated.

binlogdir

This parameter controls the location where MariaDB MaxScale stores the binary log files. This is a mandatory parameter.

The binlogdir also contains the cache subdirectory which stores data retrieved from the master during the slave registration phase. The master.ini file also resides in the binlogdir. This file keeps track of the current master configuration and it is updated when a CHANGE MASTER TO query is executed.

From 2.1 onwards, the 'cache' directory is stored in the same location as other user credential caches. This means that with the default options, the user credential cache is stored in /var/cache/maxscale/<Service Name>/<Listener Name>/cache/.

Read the MySQL Authenticator documentation for instructions on how to define a custom location for the user cache.

server_id

MariaDB MaxScale must have a unique server_id. This parameter configures the value of the server_id that MariaDB MaxScale will use when connecting to the master. This is a mandatory parameter.

Older versions of MaxScale allowed the ID to be specified using server-id. This has been deprecated and will be removed in a future release of MariaDB MaxScale.

master_id

The server_id value that MariaDB MaxScale should use to report to the slaves that connect to MariaDB MaxScale.

This may either be the same as the server id of the real master or can be chosen to be different if the slaves need to be aware of the proxy layer. The real master server ID will be used if the option is not set.

Older versions of MaxScale allowed the ID to be specified using master-id. This has been deprecated and will be removed in a future release of MariaDB MaxScale.

uuid

This is used to set the unique UUID that the binlog router uses when it connects to the master server. By default the UUID will be generated.

master_uuid

It is a requirement of replication that each server has a unique UUID value. If this option is not set, binlogrouter will identify itself to the slaves using the UUID of the real master.

master_version

By default, the router will identify itself to the slaves using the server version of the real master. This option allows the router to use a custom version string.

master_hostname

By default, the router will identify itself to the slaves using the hostname of the real master. This option allows the router to use a custom hostname.

slave_hostname

Since MaxScale 2.1.6 the router can optionally identify itself to the master using a custom hostname. The specified hostname can be seen in the master via SHOW SLAVE HOSTS command. The default is not to send any hostname string during registration.

user

Note: This is option can only be given to the router_options parameter. Use the user parameter of the service instead.

This is the user name that MariaDB MaxScale uses when it connects to the master. This user name must have the rights required for replication as with any other user that a slave uses for replication purposes. If the user parameter is not given in the router options then the same user as is used to retrieve the credential information will be used for the replication connection, i.e. the user in the service entry.

This user is the only one available for MySQL connection to MaxScale Binlog Server for administration when master connection is not done yet.

In MaxScale 2.1, the service user injection is done by the MySQLAuth authenticator module. Read the MySQL Authenticator documentation for more details.

The user that is used for replication must be granted replication privileges on the database server.

CREATE USER 'repl'@'maxscalehost' IDENTIFIED by 'password';
GRANT REPLICATION SLAVE ON *.* TO 'repl'@'maxscalehost';

password

Note: This is option can only be given to the router_options parameter. Use the password parameter of the service instead.

The password for the user. If the password is not explicitly given then the password in the service entry will be used. For compatibility with other username and password definitions within the MariaDB MaxScale configuration file it is also possible to use the parameter passwd.

heartbeat

This defines the value of the heartbeat interval in seconds for the connection to the master. The default value for the heartbeat period is every 5 minutes.

MariaDB MaxScale requests the master to ensure that a binlog event is sent at least every heartbeat period. If there are no real binlog events to send the master will sent a special heartbeat event. The current interval value is reported in the diagnostic output.

burstsize

This parameter is used to define the maximum amount of data that will be sent to a slave by MariaDB MaxScale when that slave is lagging behind the master. The default value is 1M.

The burst size can be provided as specified here, except that IEC binary prefixes can be used as suffixes only from MaxScale 2.1 onwards. MaxScale 2.0 and earlier only support burstsize defined in bytes.

In this situation the slave is said to be in "catchup mode", this parameter is designed to both prevent flooding of that slave and also to prevent threads within MariaDB MaxScale spending disproportionate amounts of time with slaves that are lagging behind the master.

mariadb10-compatibility

This parameter allows binlogrouter to replicate from a MariaDB 10.0 master server: this parameter is enabled by default since MaxScale 2.2.0. In earlier versions the parameter was disabled by default.

# Example
mariadb10-compatibility=1

Additionally, since MaxScale 2.2.1, MariaDB 10.x slave servers can connect to binlog server using GTID value instead of binlog name and position.

Example of a MariaDB 10.x slave connection to MaxScale

MariaDB> SET @@global.gtid_slave_pos='0-10122-230';
MariaDB> CHANGE MASTER TO
         MASTER_HOST='192.168.10.8',
         MASTER_PORT=5306,
         MASTER_USE_GTID=Slave_pos;
MariaDB> START SLAVE;

Note:

  • Slave servers can connect either with file and pos or GTID.

  • MaxScale saves all the incoming MariaDB GTIDs (DDLs and DMLs) in a sqlite3 database located in binlogdir (gtid_maps.db). When a slave server connects with a GTID request a lookup is made for the value match and following binlog events will be sent.

transaction_safety

This parameter is used to enable/disable incomplete transactions detection in binlog router. The default value is off.

When MariaDB MaxScale starts an error message may appear if current binlog file is corrupted or an incomplete transaction is found. During normal operations binlog events are not distributed to the slaves until a COMMIT is seen. Set transaction_safety=on to enable detection of incomplete transactions.

send_slave_heartbeat

This defines whether MariaDB MaxScale sends the heartbeat packet to the slave when there are no real binlog events to send. This parameter takes a boolean value and the default value is false. This means that no heartbeat events are sent to slave servers.

If value is set to true the interval value (requested by the slave during registration) is reported in the diagnostic output and the packet is send after the time interval without any event to send.

semisync

This parameter controls whether binlog server could ask Master server to start the Semi-Synchronous replication. This parameter takes a boolean value and the default value is false.

In order to get semi-sync working, the Master server must have the rpl_semi_sync_master plugin installed. The availability of the plugin and the value of the GLOBAL VARIABLE rpl_semi_sync_master_enabled are checked in the Master registration phase: if the plugin is installed in the Master database, the binlog server subsequently requests the semi-sync option.

Note: - the network replication stream from Master has two additional bytes before each binlog event. - the Semi-Sync protocol requires an acknowledge packet to be sent back to Master only when requested: the semi-sync flag will have value of 1. This flag is set only if rpl_semi_sync_master_enabled=1 is set in the Master, otherwise it will always have value of 0 and no ack packet is sent back.

Please note that semi-sync replication is only related to binlog server to Master communication.

ssl_cert_verification_depth

This parameter sets the maximum length of the certificate authority chain that will be accepted. Legal values are positive integers. This applies to SSL connection to master server that could be acivated either by writing options in master.ini or later via a CHANGE MASTER TO command. This parameter cannot be modified at runtime. The default verification depth is 9.

encrypt_binlog

Whether to encrypt binlog files: the default is off.

When set to on the binlog files will be encrypted using specified AES algorithm and the KEY in the specified key file.

Note: binlog encryption must be used while replicating from a MariaDB 10.1 server and serving data to MariaDB 10.x slaves. In order to use binlog encryption the master server MariaDB 10.1 must have encryption active (encrypt-binlog=1 in my.cnf). This is required because both master and maxscale must store encrypted data for a working scenario for Secure data-at-rest. Additionally, as long as Master server doesn't send the StartEncryption event (which contains encryption setup information for the binlog file), there is a position gap between end of FormatDescription event pos and next event start pos. The StartEncryption event size is 36 or 40 (depending on CRC32 being used), so the gap has that size.

MaxScale binlog server adds its own StartEncryption to binlog files consequently the binlog events positions in binlog file are the same as in the master binlog file and there is no position mismatch.

encryption_algorithm

The encryption algorithm, either 'aes_ctr' or 'aes_cbc'. The default is 'aes_cbc'

encryption_key_file

The specified key file must contains lines with following format:

id;HEX(KEY)

Id is the scheme identifier, which must have the value 1 for binlog encryption , the ';' is a separator and HEX(KEY) contains the hex representation of the KEY. The KEY must have exact 16, 24 or 32 bytes size and the selected algorithm (aes_ctr or aes_cbc) with 128, 192 or 256 ciphers will be used.

Note: the key file has the same format as MariaDB 10.1 server so it's possible to use an existing key file (not encrypted) which could contain several scheme;key values: only key id with value 1 will be parsed, and if not found an error will be reported.

Example key file with multiple keys:

#
# This is the Encryption Key File
# key id 1 is for binlog files encryption: it's mandatory
# The keys come from a 32bytes value, 64 bytes with HEX format
#
2;abcdef1234567890abcdef12345678901234567890abcdefabcdef1234567890
1;5132bbabcde33ffffff12345ffffaaabbbbbbaacccddeee11299000111992aaa
3;bbbbbbbbbaaaaaaabbbbbccccceeeddddd3333333ddddaaaaffffffeeeeecccd

mariadb10_master_gtid

This option allows MaxScale binlog router to register with MariaDB 10.X master using GTID instead of binlog_file name and position in CHANGE MASTER TO admin command. This feature is disabled by default.

The user can set a known GTID or an empty value (in this case the Master server will send events from it's first available binlog file).

Example of MaxScale connection to a MariaDB 10.X Master

# mysql -h $MAXSCALE_HOST -P $MAXCALE_PORT
MariaDB> SET @@global.gtid_slave_pos='0-198-123';
MariaDB> CHANGE MASTER TO
         MASTER_HOST='192.168.10.5',
         MASTER_PORT=3306,
         MASTER_USE_GTID=Slave_pos;
MariaDB> START SLAVE;

If using GTID request then it's no longer possible to use MASTER_LOG_FILE and MASTER_LOG_POS in CHANGE MASTER TO command: an error will be reported.

If this feature is enabled, the transaction_safety option will be automatically enabled. The binlog files will also be stored in a hierarchical directory tree instead of a single directory.

Note:

  • When the option is On, the connecting slaves can only use GTID request: specifying file and pos will end up in an error sent by MaxScale and replication cannot start.
  • The GTID request could cause the writing of events in any position of the binlog file, whose name has been sent by the master server before any event. In order to avoid holes in the binlog files, MaxScale will fill all gaps in the binlog files with ignorable events.
  • It's not possible to specify the GTID _domain_id: the master one is being used for all operations. All slave servers must use the same replication domain as the master server.

master_retry_count

This option sets the maximum number of connection retries when the master server is disconnected or not reachable. Default value is 1000.

connect_retry

The option sets the time interval for a new connection retry to master server, default value is 60 seconds.

A complete example of a service entry for a binlog router service would be as follows.

[Replication]
type=service
router=binlogrouter
user=maxscale
password=maxpwd
server_id=3
binlogdir=/var/lib/maxscale/
mariadb10-compatibility=1
encrypt_binlog=1
encryption_algorithm=aes_ctr
encryption_key_file=/var/binlogs/enc_key.txt

Using secondary masters

From MaxScale 2.3 onwards it is possible to specify secondary masters that the binlog router can use in case the connection to the default master fails.

Note: This is only supported in a Galera Cluster environment in which:

  • Wsrep GTID mode is enabled in the cluster.
  • All of the requirements for wsrep GTID mode are met by the cluster.

Wsrep GTID mode is also imperfect, so this secondary master functionality is only guaranteed to work if GTIDs have not become inconsistent within the cluster.

See Wsrep GTID Mode for more information.

The initial setup is performed exactly like when there is but one default master.

# mysql -h $MAXSCALE_HOST -P $MAXCALE_PORT
MariaDB> SET @@global.gtid_slave_pos='0-198-123';
MariaDB> CHANGE MASTER TO
         MASTER_HOST='192.168.10.5',
         MASTER_PORT=3306,
         MASTER_USER='repl',
         MASTER_PASSWORD='repl',
         MASTER_USE_GTID=Slave_pos;

After the setup of the default master, secondary masters can be configured as follows:

MariaDB> CHANGE MASTER ':2' TO
         MASTER_HOST='192.168.10.6',
         MASTER_PORT=3306,
         MASTER_USER='repl',
         MASTER_PASSWORD='repl',
         MASTER_USE_GTID=Slave_pos;

That is, a connection name must be provided and the name must be of the format :N where N is a positive integer. If several secondary masters are specified, they must be numbered consecutively, starting from 2.

All settings that are not explicitly specified are copied from the default master. That is, the following is equivalent with the command above:

MariaDB> CHANGE MASTER ':2' TO MASTER_HOST='192.168.10.6';

If a particular master configuration exists already, then any specified definitions will be changed and unspecified ones will remain unchanged. For instance, the following command would only change the password of :2.

MariaDB> CHANGE MASTER ':2' TO MASTER_PASSWORD='repl2';

It is not possible to delete a particular secondary master, but if MASTER_HOST is set on the default master, even if it is set to the same value, then all secondary master configurations are deleted.

When START SLAVE is issued, MaxScale will first attempt to connect to the default master and if that fails, try the secondary masters in order, until a connection can be created. Only if all connection attempts fail, will MaxScale wait as specified with connect_retry, before doing the cycle over again.

Once the binlog router has successfully connected to a server, it will stay connected to that server until the connection breaks or STOP SLAVE is issued.

The configurations of the secondary masters are also stored to the master.ini in sections whose name include the connection name.

[binlog_configuration]
master_host=192.168.121.150
...
[binlog_configuration:2]
master_host=192.168.121.148
...
[binlog_configuration:3]
master_host=192.168.121.76
...

Examples

The Replication Proxy tutorial will show you how to configure and administrate a binlogrouter installation.

Tutorial also includes SSL communication setup to the master server and SSL client connections setup to MaxScale Binlog Server.

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