How to refresh a single cluster¶
This guide covers refresh for single cluster MySQL deployments. To refresh a multi-cluster deployment, see How to refresh a multi-cluster deployment first.
Important information¶
Check if your current Juju version is compatible with the new charm version.
For information about charm versions, see Release notes.
To upgrade Juju, see How to upgrade Juju for a new database revision
Create and test a backup of your data before running any type of refresh. See How to create a backup.
It is recommended to integrate your application with Charmed MySQL Router. This will ensure minimal service disruption, if any.
Step 1: Record revision information¶
Note
This step is only valid when deploying from Charmhub.
If a local charm is deployed (revision is small, e.g. 0-10), make sure the proper/current local revision of the .charm file is available BEFORE going further. You might need it for a rollback.
The first step is to record the revision of the running application as a safety measure for a rollback action. To accomplish this, run the juju status command and look for the deployed Charmed MySQL revision in the command output.
Example output for Charmed MySQL on a machine controller:
Model Controller Cloud/Region Version SLA Timestamp
example lxd localhost/localhost 3.5.2 unsupported 17:58:37Z
App Version Status Scale Charm Channel Rev Exposed Message
mysql 8.0.39-0ubun... active 3 mysql 182 no
Unit Workload Agent Machine Public address Ports Message
mysql/9 active idle 13 10.169.158.70 3306/tcp,33060/tcp
mysql/10* active idle 11 10.169.158.14 3306/tcp,33060/tcp Primary
mysql/11 active idle 12 10.169.158.217 3306/tcp,33060/tcp
Machine State Address Inst id Series AZ Message
11 started 10.169.158.14 juju-b72e25-11 jammy Running
12 started 10.169.158.217 juju-b72e25-12 jammy Running
13 started 10.169.158.70 juju-b72e25-13 jammy Running
For this example, the current revision is 182. Store it safely to use in case of rollback!
Step 2: Scale up (optional)¶
With Charmed MySQL for Kubernetes, it is recommended to scale the application up by one unit before starting the upgrade process.
The new unit will be the first one to be updated, and it will assert that the upgrade is possible. In case of failure, having the extra unit will ease a future rollback procedure without disrupting service.
juju scale-application mysql-k8s <total number of units desired>
To scale up by 1 unit, <total number of units desired> would be the current number of units + 1
Wait for the new unit to be ready.
Step 3: Pre-upgrade check¶
Before refreshing, it is necessary to run the pre-upgrade-check action against the leader unit:
juju run mysql/leader pre-upgrade-check
The output of the action should look like:
unit-mysql-10:
...
results: {}
status: completed
...
juju run mysql-k8s/leader pre-upgrade-check
The output of the action should look like:
unit-mysql-k8s-0:
UnitId: mysql-k8s/0
...
results: {}
status: completed
...
Juju 2.9 users
Remember that juju run <action name> becomes juju run-action <action name> --wait.
See also: Breaking changes between Juju 2.9 and 3
The action will configure the charm to minimize the amount of primary switchover, among other preparations for a safe refresh process. After successful execution, the charm is ready to be refreshed.
Step 4: Refresh¶
If you are refreshing multiple clusters, make sure to refresh the standby clusters first. See {ref}`refresh-multi-cluster for more information.
Use the juju refresh command to trigger the charm refresh process.
Example with channel selection:
juju refresh mysql --channel 8.0/stable
Example with specific revision selection:
juju refresh mysql --revision=366
Example with a local charm file:
juju refresh mysql --path ./mysql_ubuntu-22.04-amd64.charm
Example with channel selection:
juju refresh mysql-k8s --channel 8.0/edge --trust
Example with specific revision selection( do not forget the OCI resource):
juju refresh mysql-k8s --revision=89 --resource mysql-image=... --trust
During an ongoing refresh
Do NOT perform any other extraordinary operations on the cluster, such as:
Adding or removing units
Creating or destroying new relations
Changes in workload configuration
Refreshing other connected/related/integrated applications simultaneously
Concurrency with other operations is not supported, and it can lead the cluster into inconsistent states.
Do NOT trigger a rollback. Status changes during the process are expected (e.g. waiting, maintenance, active)
Make sure the refresh has failed/stopped and cannot be continued before triggering a rollback.
Once the refresh command is executed, all units will receive new charm content. The refresh will run on one unit at a time.
After each unit completes the refresh, the message refresh completed is displayed, and the next unit follows.
Example juju status during an refresh:
Model Controller Cloud/Region Version SLA Timestamp
example lxd localhost/localhost 3.5.2 unsupported 18:11:21Z
App Version Status Scale Charm Channel Rev Exposed Message
mysql 8.0.39-0ubun... active 3 mysql 7 no
Unit Workload Agent Machine Public address Ports Message
mysql/9 maintenance executing 13 10.169.158.70 3306/tcp,33060/tcp upgrading snap...
mysql/10* waiting idle 11 10.169.158.14 3306/tcp,33060/tcp other units upgrading first...
mysql/11 maintenance idle 12 10.169.158.217 3306/tcp,33060/tcp upgrade completed
Machine State Address Inst id Series AZ Message
11 started 10.169.158.14 juju-b72e25-11 jammy Running
12 started 10.169.158.217 juju-b72e25-12 jammy Running
13 started 10.169.158.70 juju-b72e25-13 jammy Running
After the unit is upgraded, the charm will set the unit upgrade state as completed.
If the unit is healthy within the cluster, the next step is to resume the upgrade process by running:
juju run mysql-k8s/leader resume-upgrade
resume-upgrade will rollout the upgrade for the following unit, always from highest ordinal number to lowest, and for each successful upgraded unit, the process will rollout the next automatically.
Model Controller Cloud/Region Version SLA Timestamp
example k8s microk8s/localhost 3.5.2 unsupported 01:20:47Z
App Version Status Scale Charm Channel Rev Address Exposed Message
mysql-k8s 8.0.32-0ubuntu0.22.04.2 waiting 3 mysql-k8s 8.0/edge 89 10.152.183.102 no waiting for units to settle down
Unit Workload Agent Address Ports Message
mysql-k8s/0* active idle 10.1.148.184 other units upgrading first...
mysql-k8s/1 maintenance executing 10.1.148.138 upgrading unit
mysql-k8s/2 active idle 10.1.148.143
mysql-k8s/3 active idle 10.1.148.145
Please be patient during huge installations. Each unit should recover shortly after the refresh, but time can vary depending on the amount of data written to the cluster while the unit was not part of it.
Incompatible charm revisions or dependencies will halt the process.
After a juju refresh, if there are any version incompatibilities in charm revisions, its dependencies, or any other unexpected failure in the refresh process, the refresh will be halted and enter a failure state.
Step 5: Roll back¶
If there was an issue with the refresh, even if the underlying MySQL cluster continues to work, it’s important to roll back the charm to the previous revision.
The update can be attempted again after a further inspection of the failure.
Step 6: Check cluster health¶
Use juju status to make sure the cluster state is OK.