Galera Manager Daemon (gmd)¶
The Galera Manager is driven by the gmd daemon program that can create clusters, add and remove nodes, and gather monitoring data from the Galera Cluster. For information on installing gmd, see the documentation page, Installing Galera Manager.
gmd Process
If Galera Manager was installed on a host, you can enter something like the following from the command-line to check that it is running:
ps -e |grep gmd
5810 ? 00:00:18 gmd
The results showing the process identification number and the amount of time gmd has been running will be different on your server. Although it is unlikely you will need to restart gmd, to do so you may enter the following from the command-line:
systemctl restart gmd
You can replace restart with stop to shutdown the Galera Manager daemon—and use start to start it later. If the server is rebooted, gmd is set to start automatically.
Configuration File
When you installed Galera Manager, the Installer created a configuration file for gmd based on the responses you gave. You do not have to create it yourself. However, if you want to change some of the information you provided when installing, you can edit the configuration file. It is located in the sub-directory, /etc/default/ and called, gmd.
The gmd configuration file will look something like this:
ARGS="--rsa-private-key=/var/lib/gmd/jwt-rsa.key"
GMD_CONFIG_DIR=/var/lib/gmd
GMD_LOGS_DIR=/var/log/gmd
INFLUXDB_URL=https://gmd:8hCh2GeYv9@34.217.207.40:8091
PROMETHEUS_URL=https://34.217.207.40:8092
There are few settings here. You can change the values with a simple text editor. Just remember to restart gmd for the changes to take effect. See above for how to restart the daemon.
gmd Logs
In the previous section, you may have noticed the location of the log files: /var/log/gmd. Should you have difficulty starting gmd or encounter similar problems, you can check this directory for log files containing messages that may indicate the cause. Below is an example of the contents of that log file directory:
ls -1 /var/log/gmd
cluster-testeroo.log
default.log
host-hoster-jfebk-stdout.log
host-hoster-jfebk.log
host-hoster-lisvt-stdout.log
host-hoster-lisvt.log
host-hoster-mlksh-stdout.log
host-hoster-mlksh.log
node-noder-jfebk.log
node-noder-lisvt.log
node-noder-mlksh.log
There’s a log file for the gmd daemon (that is, default.log), one for the cluster, a pair for each host, and one for each node.
You may be confused as to the difference between a host and a node in this context. A host has to do with the computer system on which the Galera Cluster software is installed. This includes software configuration, network traffic, as well as where particular software like Galera Manager and MySQL are running. Whereas, a node is a database engine process running on the host and forming the Galera Cluster by connecting with other such processes running elsewhere. Is the node available and handling database client traffic? Is it synchronized with the other nodes in the cluster?
What’s important to an administrator, though, is knowing where to find log messages to troubleshoot problems that may be encountered. Below are descriptions of what may be found in each log, with the most information recorded in the host standard output log (for example, host-hoster-mlksh-stdout.log).
Default Log
The main log file for the gmd daemon, the default.log file, contains information related to starting and stopping the daemon. Here’s an excerpt from such a log file:
time="2020-05-18T08:05:19Z" level=info msg="Starting gmd"
time="2020-05-18T08:05:19Z" level=info msg="Listening on 127.0.0.1:8000"
time="2020-05-18T08:05:19Z" level=info msg="ConfigDir = /var/lib/gmd"
time="2020-05-18T08:05:19Z" level=info msg="LogsDir = /var/log/gmd"
As you can see, it records when it started the gmd daemon, on which IP address and port it is listening for connections from users (such as admin), and the directories for configuration and log files.
Cluster Log
As mentioned above, there’s a log file for the cluster. Its name contains the name of the cluster appended to it (for example, testeroo from the examples on other pages of this documentation section). This log file contains some very basic information on the settings of the cluster. Below is an example of its contents:
time="2020-06-07T06:27:39Z" level=info msg="cluster record created" cluster-name=testeroo
It is not much, since it is from a new installation of Galera Manager, one used in examples elsewhere in this documentation. It contains the date and time the cluster was created, as well as the name of the cluster. As a result of that name, this log file is named, cluster-testeroo.log.
Host Logs
As mentioned earlier, there is a pair of log files for each host in the cluster. One is labeled host, followed by the name of the host and the extension, .log This file contains primarily entries showing the data time or changes to the host’s status.
Below is an excerpt from the host-hoster-mlksh.log file from the examples used here in documentation on Galera Manager:
time="2020-06-07T06:28:58Z" level=info
msg="setting deployment status to pending" host-name=hoster-mlksh
time="2020-06-07T06:30:04Z" level=info
msg="setting deployment status to ok" host-name=hoster-mlksh
This is actually two lines of entries, but we broke the lines to fit more easily on the screen. Still, there’s not much information here. Nevertheless, you might write a custom shell script to parse this file to check for the latest entry, looking for when the deployment status is not ok, and send you a message saying as much—and then have cron run that script frequently at regular intervals. Or you could just keep Galera Manager open in a window on your computer.
The other log file for each host is labeled host, followed by the name of the host, then stdout and the extention, .log (for example, host-hoster-mlksh-stdout.log). This log file contains the messages generated by the host server when activities happen, when various commands, utilities and other programs are run by Galera Manager. If these commands and all were executed manually, some messages would normally be shown on the screen (that is, the standard output). However, since they’re run in the background, there’s no one to see them. So Galera Manager writes them to a log file for each host.
These host stdout log files are extensive. They contain information on updating Galera Manager software, network traffic, and many other logistical system information related to Galera. As a result, they can become fairly large files. But they can also be useful when trying to troubleshoot a problem with Galera Manager software—but not the synchronizing and accessing of data within the cluster, on nodes.
Node Logs
In the log directory for gmd, there is a log file for each node. As mentioned earlier, these log files contain information related to the nodes of the cluster, their interactions with each other. Below is an excerpt from the node-noder-mlksh.log file from examples elsewhere in this documentation:
time="2020-06-07T06:31:54Z" level=info msg="updating cluster IPs" ctx=update-cluster-ips node-name=noder-mlksh
time="2020-06-07T08:15:09Z" level=info msg="checking node status" node-name=noder-mlksh
time="2020-06-07T08:15:10Z" level=info msg="node status is healthy" node-name=noder-mlksh
time="2020-06-07T08:15:10Z" level=info msg="already started" node-name=noder-mlksh
Notice these entries are related to nodes in the cluster having started, being ready to accept MySQL client traffic, and in sync—that is to say, the node’s health.
Should one of the nodes have problems that are not reflected in the metrics you are tracking in Galera Manager, you could check the log for that node for an indication of what’s wrong with it. Afterwards, you might want to add the appropriate metrics to Galera Manager to monitor the situation more closely and conveniently from within Galera Manager. For more information on adding metrics to track in Galera Manager, see the Monitoring a Cluster with Galera Manager documentation page.
Galera Manager Documents
