Deploy on multiple availability zones (AZ)¶
During the deployment to hardware/VMs, it is important to spread all the database copies (Juju units) to different hardware servers, or even better, to the different availability zones (AZ). This will guarantee no shared service-critical components across the DB cluster (eliminate the case with all eggs in the same basket).
This guide will take you through deploying a PostgreSQL cluster on GCE using 3 available zones. All Juju units will be set up to sit in their dedicated zones only, which effectively guarantees database copy survival across all available AZs.
Note
This documentation assumes that your cloud supports and provides availability zones concepts. This is enabled by default on EC2/GCE and supported by LXD/MicroCloud.
Set up GCE on Google Cloud¶
Let’s deploy the PostgreSQL Cluster on GKE (us-east4) using all 3 zones there (us-east4-a, us-east4-b, us-east4-c) and make sure all pods always sits in the dedicated zones only.
Caution
Creating the following GKE resources may cost you money - be sure to monitor your GCloud costs.
Log into Google Cloud and bootstrap GCE on Google Cloud:
gcloud auth login
gcloud iam service-accounts keys create sa-private-key.json --iam-account=juju-gce-account@[your-gcloud-project-12345].iam.gserviceaccount.com
sudo mv sa-private-key.json /var/snap/juju/common/sa-private-key.json
sudo chmod a+r /var/snap/juju/common/sa-private-key.json
juju add-credential google
juju bootstrap google gce
juju add-model mymodel
Deploy PostgreSQL with Juju zones constraints¶
Juju provides support for availability zones using constraints.
The command below demonstrates how Juju automatically deploys Charmed PostgreSQL VM using Juju constraints:
juju deploy postgresql --channel 16/stable -n 3 \
--constraints zones=us-east1-b,us-east1-c,us-east1-d
After a successful deployment, juju status will show an active application:
Model Controller Cloud/Region Version SLA Timestamp
mymodel gce google/us-east1 3.5.4 unsupported 00:16:52+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 16.9 active 3 postgresql 16/stable 843 no
Unit Workload Agent Machine Public address Ports Message
postgresql/0 active idle 0 34.148.44.51 5432/tcp
postgresql/1 active idle 1 34.23.202.220 5432/tcp
postgresql/2* active idle 2 34.138.167.85 5432/tcp Primary
Machine State Address Inst id Base AZ Message
0 started 34.148.44.51 juju-e7c0db-0 [email protected] us-east1-d RUNNING
1 started 34.23.202.220 juju-e7c0db-1 [email protected] us-east1-c RUNNING
2 started 34.138.167.85 juju-e7c0db-2 [email protected] us-east1-b RUNNING
and each unit/vm will sit in the separate AZ out of the box:
> gcloud compute instances list
NAME ZONE MACHINE_TYPE PREEMPTIBLE INTERNAL_IP EXTERNAL_IP STATUS
juju-a82dd9-0 us-east1-b n1-highcpu-4 10.142.0.30 34.23.252.144 RUNNING # Juju Controller
juju-e7c0db-2 us-east1-b n2-highcpu-2 10.142.0.32 34.138.167.85 RUNNING # postgresql/2
juju-e7c0db-1 us-east1-c n2-highcpu-2 10.142.0.33 34.23.202.220 RUNNING # postgresql/1
juju-e7c0db-0 us-east1-d n2-highcpu-2 10.142.0.31 34.148.44.51 RUNNING # postgresql/0
Simulation: A node gets lost¶
Let’s destroy a GCE node and recreate it using the same AZ:
> gcloud compute instances delete juju-e7c0db-1
No zone specified. Using zone [us-east1-c] for instance: [juju-e7c0db-1].
The following instances will be deleted. Any attached disks configured to be auto-deleted will be deleted unless they are attached to any other instances or the `--keep-disks` flag is given and specifies them for keeping. Deleting a disk is
irreversible and any data on the disk will be lost.
- [juju-e7c0db-1] in [us-east1-c]
Do you want to continue (Y/n)? Y
Deleted [https://www.googleapis.com/compute/v1/projects/data-platform-testing-354909/zones/us-east1-c/instances/juju-e7c0db-1].
Model Controller Cloud/Region Version SLA Timestamp
mymodel gce google/us-east1 3.5.4 unsupported 00:25:14+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 16.9 active 2/3 postgresql 16/stable 843 no
Unit Workload Agent Machine Public address Ports Message
postgresql/0 active idle 0 34.148.44.51 5432/tcp
postgresql/1 unknown lost 1 34.23.202.220 5432/tcp agent lost, see 'juju show-status-log postgresql/1'
postgresql/2* active idle 2 34.138.167.85 5432/tcp Primary
Machine State Address Inst id Base AZ Message
0 started 34.148.44.51 juju-e7c0db-0 [email protected] us-east1-d RUNNING
1 down 34.23.202.220 juju-e7c0db-1 [email protected] us-east1-c RUNNING
2 started 34.138.167.85 juju-e7c0db-2 [email protected] us-east1-b RUNNING
Here we should remove the no-longer available server/vm/GCE node and add a new one. Juju will create it in the same AZ us-east4-c:
> juju remove-unit postgresql/1 --force --no-wait
WARNING This command will perform the following actions:
will remove unit postgresql/1
Continue [y/N]? y
The command juju status shows the machines in a healthy state, but PostgreSQL HA recovery is necessary:
Model Controller Cloud/Region Version SLA Timestamp
mymodel gce google/us-east1 3.5.4 unsupported 00:30:09+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql 16.9 active 2 postgresql 16/stable 843 no
Unit Workload Agent Machine Public address Ports Message
postgresql/0 active idle 0 34.148.44.51 5432/tcp
postgresql/2* active idle 2 34.138.167.85 5432/tcp Primary
Machine State Address Inst id Base AZ Message
0 started 34.148.44.51 juju-e7c0db-0 [email protected] us-east1-d RUNNING
2 started 34.138.167.85 juju-e7c0db-2 [email protected] us-east1-b RUNNING
Request Juju to add a new unit in the proper AZ:
juju add-unit postgresql -n 1
Juju uses the right AZ where the node is missing. Run juju status:
Model Controller Cloud/Region Version SLA Timestamp
mymodel gce google/us-east1 3.5.4 unsupported 00:30:42+02:00
App Version Status Scale Charm Channel Rev Exposed Message
postgresql active 2/3 postgresql 16/stable 843 no
Unit Workload Agent Machine Public address Ports Message
postgresql/0 active idle 0 34.148.44.51 5432/tcp
postgresql/2* active idle 2 34.138.167.85 5432/tcp Primary
postgresql/3 waiting allocating 3 waiting for machine
Machine State Address Inst id Base AZ Message
0 started 34.148.44.51 juju-e7c0db-0 [email protected] us-east1-d RUNNING
2 started 34.138.167.85 juju-e7c0db-2 [email protected] us-east1-b RUNNING
3 pending juju-e7c0db-3 [email protected] us-east1-c starting
Remove GCE setup¶
Caution
Do not forget to remove your test setup - it can be costly!
Check the list of currently running GCE instances:
> gcloud compute instances list
NAME ZONE MACHINE_TYPE PREEMPTIBLE INTERNAL_IP EXTERNAL_IP STATUS
juju-a82dd9-0 us-east1-b n1-highcpu-4 10.142.0.30 34.23.252.144 RUNNING
juju-e7c0db-2 us-east1-b n2-highcpu-2 10.142.0.32 34.138.167.85 RUNNING
juju-e7c0db-3 us-east1-c n2d-highcpu-2 10.142.0.34 34.23.202.220 RUNNING
juju-e7c0db-0 us-east1-d n2-highcpu-2 10.142.0.31 34.148.44.51 RUNNING
Request Juju to clean all GCE resources:
juju destroy-controller gce --no-prompt --force --destroy-all-models
Re-check that there are no running GCE instances left (it should be empty):
gcloud compute instances list