AZ-305 business continuity explained
Design business continuity solutions is worth 15–20% of AZ-305. It has two halves: backup and disaster recovery, and high availability. Almost every question can be solved by reading two numbers from the scenario, the recovery point objective (RPO, how much data you can lose) and the recovery time objective (RTO, how long you can be down), and then choosing the cheapest design that meets both.
Start with the objectives
| Term | Question it answers |
|---|---|
| RPO | How much recent data can we afford to lose? |
| RTO | How long can the service be unavailable? |
| Availability target | What percentage of the time must the service be up? |
Tighter objectives cost more. A request for an RPO of seconds rules out daily backups; an RTO of minutes rules out restoring from backup into an empty region. Recommend per tier: a reporting database seldom needs the same design as the order system.
Backup and disaster recovery
Azure Backup
Azure Backup protects VMs, SQL Server and SAP HANA in VMs, Azure Files and, through a Backup vault, blobs, managed disks and some database services. The key choice is the vault type:
| Vault | Typical workloads |
|---|---|
| Recovery Services vault | Azure VMs, workloads inside VMs, Azure Files, on-premises machines, Site Recovery |
| Backup vault | Azure Disks, Blob Storage, PostgreSQL and other newer workload types |
Backups give a restore point, so they define RPO. For stronger protection, recommend soft delete, immutable vaults, multi-user authorisation and cross-region restore.
Azure Site Recovery
Site Recovery replicates VMs continuously to another region (or from on-premises to Azure) and fails them over when needed. It suits “RTO of an hour, RPO of minutes” for VM-based workloads, supports recovery plans that start tiers in order, and allows non-disruptive test failovers. It is not a backup: it replicates corruption too, which is why you pair it with Azure Backup.
Databases and unstructured data
- Azure SQL Database has automated backups with point-in-time restore and long-term retention. Geo-restore recovers from the last geo-replicated backup; active geo-replication or failover groups keep a readable secondary in another region for much lower RPO and RTO, and failover groups add an endpoint that does not change.
- Cosmos DB offers periodic or continuous backup, and multi-region accounts with automatic failover.
- Blob Storage relies on redundancy for durability and on soft delete, versioning, point-in-time restore and immutability for recovery from human error.
High availability
Compute
A single VM in a single datacenter is a single point of failure. Choose, in order of strength:
- Availability sets spread VMs across fault and update domains inside one datacenter.
- Availability zones spread them across physically separate datacenters in a region, which is the usual recommendation for a zone-level failure.
- Multiple regions with a global load balancer, for a regional outage.
PaaS services often offer zone redundancy as a setting, such as App Service plans and Azure SQL Database. Check whether a service is zonal, zone-redundant or regional-only before recommending it.
Relational data
Zone-redundant configurations of Azure SQL Database and Managed Instance survive the loss of a datacenter. For regional protection use failover groups. SQL Server on VMs needs an always-on availability group across zones.
Semi-structured and unstructured data
Pick the redundancy that matches the failure you must survive:
| Failure | Minimum option |
|---|---|
| Disk or rack | LRS |
| Datacenter | ZRS |
| Region | GRS or GZRS |
| Read during a regional outage | RA-GRS or RA-GZRS |
Cosmos DB gets high availability from adding regions and enabling automatic failover.
Worked example
A booking system has a web tier, an Azure SQL database and uploaded documents. The business accepts losing five minutes of data and four hours of downtime in a regional disaster, but expects no downtime for a datacenter failure. A sound design: zone-redundant App Service and database in the primary region, a failover group to a secondary region, RA-GZRS for documents, and Azure Backup with long-term retention for compliance.
Practice questions
Question 1. A company runs a business-critical Azure SQL database. A regional outage must be recoverable with data loss of seconds and without changing the connection string in the application. What should you recommend?
- A. Geo-restore from the automated backups
- B. Local automated backups with a longer retention period
- C. A copy of the database exported nightly to Blob Storage
- D. An auto-failover group with a secondary region
Show answer
Answer: D
A failover group replicates to a secondary region asynchronously with very small data loss and exposes read-write and read-only listener endpoints that stay the same after failover. Geo-restore has a larger RPO and slower RTO. Local backups cannot help with a regional outage. A longer retention period does not provide failover.
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Question 2. A line-of-business application runs on two VMs in one region. The business wants the application to survive the failure of an entire datacenter in that region with no downtime and no data replication to other regions. What should you recommend?
- A. Deploy the VMs across availability zones behind a load balancer
- B. Place both VMs in one availability set
- C. Back up the VMs daily with Azure Backup
- D. Resize both VMs to a larger size
Show answer
Answer: A
Spreading the VMs across availability zones puts them in separate datacenters within the region and keeps the application running if one zone fails. An availability set stays within one datacenter. Azure Backup restores after a failure but does not prevent downtime. A larger VM size does not add redundancy.
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Question 3. An organisation replicates its on-premises VMware virtual machines to Azure for disaster recovery. The RPO is 15 minutes and the RTO is 2 hours. The team wants to rehearse failover without disturbing production. Which service should you recommend?
- A. Azure Backup with a daily schedule
- B. Azure Migrate with a one-time migration
- C. Azure Site Recovery with a recovery plan
- D. Manual snapshots stored in a storage account
Show answer
Answer: C
Azure Site Recovery replicates on-premises machines to Azure continuously, supports recovery plans and allows test failovers without affecting production. Azure Backup restores from backup points and cannot reach a 15-minute RPO or rehearse a failover in this way. Azure Migrate assesses and migrates but is not a standing DR service. A storage account snapshot does not protect VM configuration.
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What to do next
Move to the largest domain with the infrastructure guide. The storage redundancy table in the cheat sheet is worth memorising.