Register trainee teachers - Disaster recovery
This documentation covers two scenarios:
In case of any of the above database disaster scenarios, please do the following:
Freeze pipeline
Alert all developers that no one should merge to main branch.
Local Dependencies
You will need the following tools installed to successfully complete the process:
When testing against a review environment (e.g. ending pr-1234) add APP_NAME=1234 to the end of any make review... commands.
Maintenance mode
In the instance of data loss it will probably be desirable to enable Maintenance mode to ensure that the database is only read from and written to when it is back in it's expected state.
Set up a virtual meeting
Set up a virtual meeting via Zoom, Slack, Teams or Google Meet, inviting all the relevant technical stakeholders. Regularly provide updates on the #twd_publish Slack channel to keep product owners abreast of developments.
Internet Connection
Ensure whoever is executing the process has a reliable and reasonably fast Internet connection.
Loss of database instance
In case the database instance is lost, the objectives are:
- Recreate the lost postgres database instance
- Restore data from nightly backup stored in Azure. The point-in-time and snapshot backups created by the PaaS Postgres service will not be available if it's been deleted.
Recreate the lost postgres database instance
Please note, this process should take about 25 mins* to complete. In case the database service is deleted or in an inconsistent state we must recreate it and repopulate it.
First make sure it is fully gone by running:
cf services | grep register-postgres
# check output for lost or corrupted instance
cf delete-service <instance-name>
N.B. When testing the cf delete-service <instance name> in the review environment the postgres service key needs deleting first. Retrieve the service key with cf service-keys <instance name> and then delete the service key using cf delete-service-key <instance name> <service key name>
Then recreate the lost postgres database instance using the following make recipes deploy-plan and deploy. Replacing the qa in the app name below with pr-1234 when testing in the review environment. To see the proposed changes:
TAG=$(cf app register-<env> | awk -F : '$1 == "docker image" {print $3}')
make <env> deploy-plan PASSCODE=<my-passcode> IMAGE_TAG=${TAG} [CONFIRM_PRODUCTION=YES]
To apply proposed changes i.e. create new database instance:
TAG=$(cf app register-<env> | awk -F : '$1 == "docker image" {print $3}')
make <env> deploy PASSCODE=<my-passcode> IMAGE_TAG=${TAG} [CONFIRM_PRODUCTION=YES]
This will create a new postgres database instance as described in the terraform configuration file.
* ~20 minutes to recreate postgres instance and ~5 min restore time when testing process in QA
Restore Data From Nightly Backup
You will need to be logged into GovUK PaaS and Azure using the az and cf CLIs. You will need to raise a PIM request to elevate your credentials for a production restore. A collegue will need to approve this for you.
Once the lost database instance has been recreated, the last nightly backup will need to be restored. To achieve this, use the following makefile recipe: restore-data-from-nightly-backup. The following will need to be set: CONFIRM_PRODUCTION=YES, CONFIRM_RESTORE=YES and BACKUP_DATE="yyyy-mm-dd".
The make recipe restore-data-from-nightly-backup executes 2 scripts, these should be committed with the execute permission (755) set but these may have been inadvertently altered. If you get a permissions error executing them run chmod +x <path/to/script>.
When testing this step against a review environment a manual backup will need to be created from the review postgres instance. Use the make receipe backup-review-database by executing make review backup-review-database APP_NAME=1234. This can then be uploaded to the backup Azure storage container by executing make review upload-review-backup BACKUP_DATE="yyyy-mm-dd" APP_NAME=1234.
# space is the name of the environment in GOV.UK PaaS, eg 'bat-prod'
# env is the target environment in the make file e.g. 'production'
az login
cf login -o dfe -s <space> -u my.name@education.gov.uk
make <env> restore-data-from-nightly-backup BACKUP_DATE="yyyy-mm-dd" CONFIRM_PRODUCTION=YES CONFIRM_RESTORE=YES
This will download the latest daily backup from Azure Storage and then populate the new database with data. If more than one backup has been created on the date specified the script will select the most recent from that date.
During the restore process a number of errors are expected because the permission level being used is not high enough to perform actions on certain database objects. These are listed below:
ERROR: must be owner of event trigger reassign_owned (or make_readable, forbid_ddl_reader)
ERROR: must be owner of function public.reassign_owned (or public.make_readable_generic, public.make_readable, public.forbid_ddl_reader)
ERROR: must be owner of extension uuid-ossp (or pgcrypto, citext, btree_gist, btree_gin)
ERROR: function "forbid_ddl_reader" already exists with same argument types (or "make_readable", "make_readable_generic", "reassign_owned")
ERROR: permission denied for table spatial_ref_sys
ERROR: permission denied to create event trigger "forbid_ddl_reader" (or "make_readable", "reassign_owned")
Data Loss
In the case of a data loss, we need to recover the data as soon as possible in order to resume normal service. Declare a major incident and document the incident timelines as you go along. It is not currently possible to test the data loss scenario with a review environment.
The application's database is a postgres instance, which resides on PaaS. This provides a point-in-time backup with the resolution of 1 second, available between 5min and 7days. We can use terraform to create a new database instance and use a point-in-time backup from the corrupted instance to restore the data. This will be done in a single terraform apply operation.
Make note of database failure time
Make note of the time the database failure occurred, and then use this to calculate when the integrity of the data in the database was still viable. For instance, if data loss or corruption happened at 1200hrs, use this to work out what snapshot time is best for the product (consult with the PM if you are unsure what would be best from the product perspective). This would determine the value of SNAPSHOT_TIME env.
Important: You should convert the time to UTC before actually using it. When you record the time, note what timezone you are using. Especially during BST (British Summer Time).
Get affected postgres database ID
Use the makefile's get-postgres-instance-guid to get the database guid, use the following command:
make <env> get-postgres-instance-guid [CONFIRM_PRODUCTION=true]
env is the target environment e.g. production
Rename postgres database instance service
Rename the affected database instance so a new database can be recreated with the production name. To achieve this, run the following make command
make <env> rename-postgres-service passcode=xxxx [CONFIRM_PRODUCTION=true]
this renames the database by appending "-old" to the database name, env is the target environment e.g. production, obtain a passcode from GOV.UK PaaS one-time passcode
Remove affected postgres database instance from terraform state file
In order for terraform to be able to create a new database instance, the existing database reference needs to be removed from the state file. This is to ensure it is no longer managed by terraform, otherwise, terraform would revert our changes. To achieve this, use the makefile target -
az login # authenticate to Azure because statefile is in an Azure Storage Container
make <env> remove-postgres-tf-state [CONFIRM_PRODUCTION=true]
env is the target environment e.g. production
Restore postgres database instance
The following variables need to be set: DB_INSTANCE_GUID (the output of the 'Get affected postgres instance guid' step, SNAPSHOT_TIME ("2021-09-14 16:00:00" IMPORTANT - this is UTC time!), passcode (a passcode from GOV.UK PaaS one-time passcode), CONFIRM_PRODUCTION (true) and tag (the docker tag for the application image).
The following commands combine the makefile recipes above to initiate the restore process by using the approriate variable values:
# env is the target environment in the make file e.g. 'production'
# space is the name of the environment in GOV.UK PaaS, eg 'bat-prod'
az login
cf login -o dfe -s <space> -u my.name@education.gov.uk
PASSCODE=xxxx # obtain from https://login.london.cloud.service.gov.uk/passcode
DB_INSTANCE_GUID=$(make <env> get-postgres-instance-guid)
TAG=$(make <env> get-image-tag)
make <env> rename-postgres-service PASSCODE=${PASSCODE} CONFIRM_PRODUCTION=true
make <env> remove-postgres-tf-state PASSCODE=${PASSCODE} CONFIRM_PRODUCTION=true
make <env> restore-postgres DB_INSTANCE_GUID=${DB_INSTANCE_GUID} SNAPSHOT_TIME="yyyy-mm-dd HH:MM:ss" PASSCODE=${PASSCODE} IMAGE_TAG=${TAG} CONFIRM_PRODUCTION=true
You will be prompted to review the terraform plan. Check for the following:
- the
cloudfoundry_app.docker_imagetags are not changing - a new database instance is being created using a point-in-time database backup of corrupted database
- new service keys are created
The restore process should take ~25 min. Terraform should write logs to the console with progress, the bulk of the time will be spent recreating the postgres instance.
Reboot postgres database instance
[PaaS docs]{https://docs.cloud.service.gov.uk/deploying_services/postgresql/#reboot-a-postgresql-service-instance}
This will take a few minutes of downtime
cf update-service SERVICE_NAME -c '{"reboot": true}'
Failover postgres database instance
High availability plans can be failed over to the replica
[PaaS docs]{https://docs.cloud.service.gov.uk/deploying_services/postgresql/#reboot-a-postgresql-service-instance}
cf update-service SERVICE_NAME -c '{"reboot": true, "force_failover": true}'
PaaS documentation
Gov UK PaaS Documentation on Point-in-time database recovery can be found here
Tidy up
Once the database has been successfully restored, the corrupted database instance should be deleted.
cf delete-service register-postgres-<env>-old -f