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A configurable tag framework is available to allow the metadata of InnoDB Cluster, InnoDB ClusterSet, or InnoDB ReplicaSet to be marked with additional information. Tags make it possible to associate custom key-value pairs to a Cluster, ReplicaSet, or instance. Tags have been reserved for use by MySQL Router that enables a compatible MySQL Router to support hiding instances from applications. The following tags are reserved for this purpose:
_hiddeninstructs MySQL Router: Excludes the instance from the list of possible destinations for client applications._disconnect_existing_sessions_when_hidden: Instructs the router to disconnect existing connections from instances that are marked to be hidden.
For more information, see Removing Instances from Routing.
In addition, the tags framework is user-configurable. Custom tags
can consist of any ASCII character and provide a
namespace, which serves as a dictionary
key-value pairs that can be associated with Clusters, ReplicaSets,
or their specific instances. Tag values can be any JSON value.
This configuration enables you to add your own attributes on top
of the metadata.
The
Cluster.options()myCluster could show:
mysql-js> myCluster.options()
{
"cluster": {
"name": "test1",
"tags": {
"ic-1:3306": [
{
"option": "_disconnect_existing_sessions_when_hidden",
"value": true
},
{
"option": "_hidden",
"value": false
}
],
"ic-2:3306": [],
"ic-3:3306": [],
"global": [
{
"option": "location:",
"value": "US East"
}
]
}
}
}
This cluster has a global tag named location
which has the value US East, and instance
ic-1 has been tagged.
You can set tags at the instance level, which enables you for
example to mark an instance as not available, so that
applications and router treat it as offline. Use the
Cluster.setInstanceOption(instance,
option,
value)
The instance argument is a connection
string to the target instance. The
option argument must be a string with
the format
namespace:optionvalue parameter is the value that
should be assigned to option in the specified
namespace. If the value is
null, the option is
removed from the specified namespace. For
instances which belong to a cluster, the
setInstanceOption() operation only accepts
the tag namespace. Any other namespace
results in an ArgumentError.
For example, to use JavaScript to set the tag
test to true on
the myCluster instance
ic-1, issue:
mysql-js> myCluster.setInstanceOption("icadmin@ic-1:3306", "tag:test", true);
Or using Python to set the tag test
to true on the
myCluster instance
ic-1, issue:
mysql-py> myCluster.set_instance_option("icadmin@ic-1:3306", "tag:test", True);When AdminAPI and MySQL Router are working together, they support specific tags that enable you to mark instances as hidden and remove them from routing. MySQL Router then excludes such tagged instances from the routing destination candidates list. This functionality enables you to safely take a server instance offline so that applications and MySQL Router ignore it. For example, while you perform maintenance tasks, such as a server upgrade or configuration changes.
When the _hidden tag is set to true, this
instructs MySQL Router to exclude the instance from the list of
possible destinations for client applications. The instance
remains online, but is not routed to for new incoming
connections. The
_disconnect_existing_sessions_when_hidden tag
controls how existing connections to the instance are closed.
This tag is assumed to be true, and it instructs any MySQL Router
instances bootstrapped against the InnoDB Cluster,
InnoDB ClusterSet, or InnoDB ReplicaSet to disconnect any
existing connections from the instance when the
_hidden tag is true.
When
_disconnect_existing_sessions_when_hidden is
false, any existing client connections to the instance are not
closed if _hidden is true. The reserved
_hidden and
_disconnect_existing_sessions_when_hidden
tags are specific to instances and cannot be used at the cluster
level.
Warning
When the
use_gr_notifications
MySQL Router option is enabled, it defaults to 60 seconds. This
means that when you set tags, it takes up to 60 seconds for
MySQL Router to detect the change. To reduce the waiting time,
change
use_gr_notifications to a
lower value.
For example, suppose you want to remove the
ic-1 instance which is part of an
InnoDB Cluster assigned to myCluster from
the routing destinations. Use the
setInstanceOption() JavaScript operation to
enable the _hidden and
_disconnect_existing_sessions_when_hidden
tags:
mysql-js> myCluster.setInstanceOption("icadmin@ic-1:3306", "tag:_hidden", true);
Or use the set_instance_option() Python
operation to enable the _hidden and
_disconnect_existing_sessions_when_hidden
tags:
mysql-js> myCluster.set_instance_option("icadmin@ic-1:3306", "tag:_hidden", true);
You can verify the change in the metadata by checking the
options. For example the change made to ic-1
would show in the options as:
mysql-js> myCluster.options()
{
"cluster": {
"name": "test1",
"tags": {
"ic-1:3306": [
{
"option": "_disconnect_existing_sessions_when_hidden",
"value": true
},
{
"option": "_hidden",
"value": true
}
],
"ic-2:3306": [],
"ic-3:3306": [],
"global": []
}
}
}
You can verify that MySQL Router has detected the change in the
metadata by viewing the log file. A MySQL Router that has detected
the change made to ic-1 would show a change
such as:
2020-07-03 16:32:16 metadata_cache INFO [7fa9d164c700] Potential changes detected in cluster 'testCluster' after metadata refresh
2020-07-03 16:32:16 metadata_cache INFO [7fa9d164c700] view_id = 4, (3 members)
2020-07-03 16:32:16 metadata_cache INFO [7fa9d164c700] ic-1:3306 / 33060 - mode=RW
2020-07-03 16:32:16 metadata_cache INFO [7fa9d164c700] ic-1:3306 / 33060 - mode=RO
2020-07-03 16:32:16 metadata_cache INFO [7fa9d164c700] ic-1:3306 / 33060 - mode=RO hidden=yes disconnect_when_hidden=yes
2020-07-03 16:32:16 routing INFO [7fa9d164c700] Routing routing:testCluster_x_ro listening on 64470 got request to disconnect invalid connections: metadata change
2020-07-03 16:32:16 routing INFO [7fa9d164c700] Routing routing:testCluster_x_rw listening on 64460 got request to disconnect invalid connections: metadata change
2020-07-03 16:32:16 routing INFO [7fa9d164c700] Routing routing:testCluster_rw listening on 6446 got request to disconnect invalid connections: metadata change
2020-07-03 16:32:16 routing INFO [7fa9d164c700] Routing routing:testCluster_ro listening on 6447 got request to disconnect invalid connections: metadata change
To bring the instance back online, use the
setInstanceOption() operation to remove the
tags, and MySQL Router automatically adds the instance back to the
routing destinations, and it becomes online for applications.
For example:
mysql-js> myCluster.setInstanceOption(icadmin@ic-1:3306, "tag:_hidden", false);Verify the change in the metadata by checking the options again:
mysql-js> myCluster.options()
{
"cluster": {
"name": "test1",
"tags": {
"ic-1:3306": [
{
"option": "_disconnect_existing_sessions_when_hidden",
"value": true
},
{
"option": "_hidden",
"value": false
}
],
"ic-2:3306": [],
"ic-3:3306": [],
"global": []
}
}
}
You can also view the _hidden status on
members using the attribute hiddenFromRouter
in the output of the following commands:
Cluster.status()Cluster.describe()ReplicaSet.status()
This attribute is true for any member hidden
from MySQL Router traffic using the _hidden
metadata tag.
The
Cluster.setOption(option,
value)option argument must be
a string with the format
namespace:option
The value parameter is the value to
be assigned to option in the specified
namespace. If the value is
null, the option is
removed from the specified namespace. For
Clusters, the setOption() operation accepts
the tag namespace. Any other namespace
results in an ArgumentError.
Tip
Tags set at the cluster level do not override tags set at the
instance level. You cannot use
Cluster.setOption()
There is no requirement for all the instances to be online, only
that the cluster has quorum.
To tag the InnoDB Cluster assigned to
myCluster with the
location tag set to US East, issue the
following in JavaScript:
mysql-js> myCluster.setOption("tag:location", "US East")
mysql-js> myCluster.options()
{
"cluster": {
"name": "test1",
"tags": {
"ic-1:3306": [],
"ic-2:3306": [],
"ic-3:3306": [],
"global": [
{
"option": "location:",
"value": "US East"
}
]
}
}
}Or issue the following in Python:
mysql-py> myCluster.set_option("tag:location", "US East")
mysql-pys> myCluster.options()
{
"cluster": {
"name": "test1",
"tags": {
"ic-1:3306": [],
"ic-2:3306": [],
"ic-3:3306": [],
"global": [
{
"option": "location:",
"value": "US East"
}
]
}
}
}
To remove a tag from a Cluster, use the
Cluster.setOption(option,
value)null value in JavaScript, and a None
value in Python.
To remove the tag from InnoDB Cluster assigned to
myCluster with the
location tag, issue the following in
JavaScript:
mysql-js> myCluster.setOption("tag:location", null)Or using Python:
mysql-js> myCluster.set_option("tag:location", None)
AdminAPI supports the tag namespace, where
you can store information in the key-value pairs associated with
a given Cluster, ReplicaSet or instance. The options under the
tag namespace are not constrained, meaning
you can tag with whatever information you choose, as long as it
is a valid MySQL ASCII identifier.
You can use any name and value for a tag, as long as the name follows the following syntax: _ or letters followed by alphanumeric and _ characters.
The namespace option is a colon separated
string with the format namespace:option,
where namespace is the name of the namespace
and option is the actual option name. You can
set and remove tags at the instance level, or at the Cluster or
ReplicaSet level.
Tag names can have any value as long as it starts with a letter
or underscore, optionally followed by alphanumeric and
_ characters, for example,
^[a-zA-Z_][0-9a-zA-Z_]*. Only built-in tags
are allowed to start with the underscore _
character.
How you use custom tags is up to you. You could set a custom tag
on a Cluster to mark the location of the Cluster. For example,
set a custom tag named location with a value of
EMEA on the Cluster.