MaxScale 21.06 Common Monitor Parameters
Common Monitor Parameters
This document lists optional parameters that all current monitors support.
Parameters
user
Username used by the monitor to connect to the backend servers. If a server defines
the monitoruser
parameter, that value will be used instead.
password
Password for the user defined with the user
parameter. If a server defines
the monitorpw
parameter, that value will be used instead.
Note: In older versions of MaxScale this parameter was called passwd
. The
use of passwd
was deprecated in MaxScale 2.3.0.
monitor_interval
- Type: duration
- Default: 2s
- Dynamic: Yes
Defines how often the monitor updates the status of the servers. Choose a lower
value if servers should be queried more often. The smallest possible value is
100 milliseconds. If querying the servers takes longer than monitor_interval
,
the effective update rate is reduced.
monitor_interval=2s
The interval is specified as documented here. If no explicit unit is provided, the value is interpreted as milliseconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected.
backend_connect_timeout
- Type: duration
- Default: 3s
- Dynamic: Yes
This parameter controls the timeout for connecting to a monitored server. The interval is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second. The minimum value is 1 second.
backend_connect_timeout=3s
backend_write_timeout
- Type: duration
- Default: 3s
- Dynamic: Yes
This parameter controls the timeout for writing to a monitored server. The timeout is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second. The minimum value is 1 seconds.
backend_write_timeout=3s
backend_read_timeout
- Type: duration
- Default: 3s
- Dynamic: Yes
This parameter controls the timeout for reading from a monitored server. The timeout is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second. The minimum value is 1 second.
backend_read_timeout=3s
backend_connect_attempts
- Type: integer
- Default: 1
- Dynamic: Yes
This parameter defines the maximum times a backend connection is attempted every
monitoring loop. Every attempt may take up to backend_connect_timeout
seconds
to perform. If none of the attempts are successful, the backend is considered to
be unreachable and down.
backend_connect_attempts=1
disk_space_threshold
This parameter duplicates the disk_space_threshold
server parameter.
If the parameter has not been specified for a server, then the one specified
for the monitor is applied.
NOTE: Since MariaDB 10.4.7, MariaDB 10.3.17 and MariaDB 10.2.26, the
information will be available only if the monitor user has the FILE
privilege.
That is, if the disk configuration is the same on all servers monitored by the monitor, it is sufficient (and more convenient) to specify the disk space threshold in the monitor section, but if the disk configuration is different on all or some servers, then the disk space threshold can be specified individually for each server.
For example, suppose server1
, server2
and server3
are identical
in all respects. In that case we can specify disk_space_threshold
in the monitor.
[server1] type=server ... [server2] type=server ... [server3] type=server ... [monitor] type=monitor servers=server1,server2,server3 disk_space_threshold=/data:80 ...
However, if the servers are heterogeneous with the disk used for the data directory mounted on different paths, then the disk space threshold must be specified separately for each server.
[server1] type=server disk_space_threshold=/data:80 ... [server2] type=server disk_space_threshold=/Data:80 ... [server3] type=server disk_space_threshold=/DBData:80 ... [monitor] type=monitor servers=server1,server2,server3 ...
If most of the servers have the data directory disk mounted on the same path, then the disk space threshold can be specified on the monitor and separately on the server with a different setup.
[server1] type=server disk_space_threshold=/DbData:80 ... [server2] type=server ... [server3] type=server ... [monitor] type=monitor servers=server1,server2,server3 disk_space_threshold=/data:80 ...
Above, server1
has the disk used for the data directory mounted
at /DbData
while both server2
and server3
have it mounted on
/data
and thus the setting in the monitor covers them both.
disk_space_check_interval
- Type: duration
- Default: 0s
- Dynamic: Yes
With this parameter it can be specified the minimum amount of time between disk space checks. The interval is specified as documented here. If no explicit unit is provided, the value is interpreted as milliseconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. The default value is 0, which means that by default the disk space will not be checked.
Note that as the checking is made as part of the regular monitor interval
cycle, the disk space check interval is affected by the value of
monitor_interval
. In particular, even if the value of
disk_space_check_interval
is smaller than that of monitor_interval
,
the checking will still take place at monitor_interval
intervals.
script
- Type: string
- Default: none
- Dynamic: Yes
This command will be executed on a server state change. The parameter should be an absolute path to a command or the command should be in the executable path. The user running MaxScale should have execution rights to the file itself and the directory it resides in. The script may have placeholders which MaxScale will substitute with useful information when launching the script.
The placeholders and their substitution results are:
$INITIATOR
-> IP and port of the server which initiated the event$EVENT
-> event description, e.g. "server_up"$LIST
-> list of IPs and ports of all servers$NODELIST
-> list of IPs and ports of all running servers$SLAVELIST
-> list of IPs and ports of all slave servers$MASTERLIST
-> list of IPs and ports of all master servers$SYNCEDLIST
-> list of IPs and ports of all synced Galera nodes$PARENT
-> IP and port of the parent of the server which initiated the event. For master-slave setups, this will be the master if the initiating server is a slave.$CHILDREN
-> list of IPs and ports of the child nodes of the server who initiated the event. For master-slave setups, this will be a list of slave servers if the initiating server is a master.
The expanded variable value can be an empty string if no servers match the
variable's requirements. For example, if no masters are available $MASTERLIST
will expand into an empty string. The list-type substitutions will only contain
servers monitored by the current monitor.
script=/home/user/myscript.sh initiator=$INITIATOR event=$EVENT live_nodes=$NODELIST
The above script could be executed as:
/home/user/myscript.sh initiator=[192.168.0.10]:3306 event=master_down live_nodes=[192.168.0.201]:3306,[192.168.0.121]:3306
See section Script example below for an example script.
Any output by the executed script will be logged into the MaxScale log. Each outputted line will be logged as a separate log message.
The log level on which the messages are logged depends on the format of the
messages. If the first word in the output line is one of alert:
, error:
,
warning:
, notice:
, info:
or debug:
, the message will be logged on the
corresponding level. If the message is not prefixed with one of the keywords,
the message will be logged on the notice level. Whitespace before, after or
between the keyword and the colon is ignored and the matching is
case-insensitive.
Currently, the script must not execute any of the following MaxCtrl calls as they cause a deadlock:
alter monitor
to the monitor executing the scriptstop monitor
to the monitor executing the scriptcall command
to a MariaDB-Monitor that is executing the script
script_timeout
- Type: duration
- Default: 90s
- Dynamic: Yes
The timeout for the executed script. The interval is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the timeout is seconds, a timeout specified in milliseconds will be rejected, even if the duration is longer than a second.
If the script execution exceeds the configured timeout, it is stopped by sending a SIGTERM signal to it. If the process does not stop, a SIGKILL signal will be sent to it once the execution time is greater than twice the configured timeout.
events
- Type: enum
- Dynamic: Yes
- Values:
master_down
,master_up
,slave_down
,slave_up
,server_down
,server_up
,lost_master
,lost_slave
,new_master
,new_slave
- Default: All events
A list of event names which cause the script to be executed. If this option is not defined, all events cause the script to be executed. The list must contain a comma separated list of event names.
events=master_down,slave_down
The following table contains all the possible event types and their descriptions.
Event Name | Description |
---|---|
master_down | A Master server has gone down |
master_up | A Master server has come up |
slave_down | A Slave server has gone down |
slave_up | A Slave server has come up |
server_down | A server with no assigned role has gone down |
server_up | A server with no assigned role has come up |
lost_master | A server lost Master status |
lost_slave | A server lost Slave status |
new_master | A new Master was detected |
new_slave | A new Slave was detected |
journal_max_age
- Type: duration
- Default: 28800s
- Dynamic: Yes
The maximum journal file age. The interval is specified as documented here. If no explicit unit is provided, the value is interpreted as seconds in MaxScale 2.4. In subsequent versions a value without a unit may be rejected. Note that since the granularity of the max age is seconds, a max age specified in milliseconds will be rejected, even if the duration is longer than a second.
When the monitor starts, it reads any stored journal files. If the journal file is older than the value of journal_max_age, it will be removed and the monitor starts with no prior knowledge of the servers.
Monitor Crash Safety
Starting with MaxScale 2.2.0, the monitor modules keep an on-disk journal of the latest server states. This change makes the monitors crash-safe when options that introduce states are used. It also allows the monitors to retain stateful information when MaxScale is restarted.
For MySQL monitor, options that introduce states into the monitoring process are
the detect_stale_master
and detect_stale_slave
options, both of which are
enabled by default. Galeramon has the disable_master_failback
parameter which
introduces a state.
The default location for the server state journal is in
/var/lib/maxscale/<monitor name>/monitor.dat
where <monitor name>
is the
name of the monitor section in the configuration file. If MaxScale crashes or is
shut down in an uncontrolled fashion, the journal will be read when MaxScale is
started. To skip the recovery process, manually delete the journal file before
starting MaxScale.
Script example
Below is an example monitor configuration which launches a script with all supported substitutions. The example script reads the results and prints it to file and sends it as email.
[MyMonitor] type=monitor module=mariadbmon servers=C1N1,C1N2,C1N3 user=maxscale password=password monitor_interval=10000 script=/path/to/maxscale_monitor_alert_script.sh --initiator=$INITIATOR --parent=$PARENT --children=$CHILDREN --event=$EVENT --node_list=$NODELIST --list=$LIST --master_list=$MASTERLIST --slave_list=$SLAVELIST --synced_list=$SYNCEDLIST
File "maxscale_monitor_alert_script.sh":
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 | #!/usr/bin/env bash initiator="" parent="" children="" event="" node_list="" list="" master_list="" slave_list="" synced_list="" process_arguments() { while [ "$1" != "" ]; do if [[ "$1" =~ ^--initiator=.* ]]; then initiator=${1#'--initiator='} elif [[ "$1" =~ ^--parent.* ]]; then parent=${1#'--parent='} elif [[ "$1" =~ ^--children.* ]]; then children=${1#'--children='} elif [[ "$1" =~ ^--event.* ]]; then event=${1#'--event='} elif [[ "$1" =~ ^--node_list.* ]]; then node_list=${1#'--node_list='} elif [[ "$1" =~ ^--list.* ]]; then list=${1#'--list='} elif [[ "$1" =~ ^--master_list.* ]]; then master_list=${1#'--master_list='} elif [[ "$1" =~ ^--slave_list.* ]]; then slave_list=${1#'--slave_list='} elif [[ "$1" =~ ^--synced_list.* ]]; then synced_list=${1#'--synced_list='} fi shift done } process_arguments $@ read -r -d '' MESSAGE << EOM A server has changed state. The following information was provided: Initiator: $initiator Parent: $parent Children: $children Event: $event Node list: $node_list List: $list Master list: $master_list Slave list: $slave_list Synced list: $synced_list EOM # print message to file echo "$MESSAGE" > /path/to/script_output.txt # email the message echo "$MESSAGE" | mail -s "MaxScale received $event event for initiator $initiator." mariadb_admin@domain.com |