Among its abundant features, a major capacity includes executing manual failovers for transferring single master write regions. For the professionals preparing for the DP-420 exam, understanding this functionality is paramount as it furnishes a competitive edge in designing and implementing native applications using Cosmos DB.
Failover Concepts in Azure Cosmos DB
Azure Cosmos DB offers multi-master and single-master modes. In the single-master mode, one region is selected as the write region, while the supplementary regions serve as read-regions. There are automatic and manual failovers for managing outages. Manual failover, as the name insinuates, requires user interference to switch the write-region.
Manual failovers are beneficial in many situations:
- To test your application’s ability to recuperate from regional disasters.
- To relocate the write region closer to the maximum load.
- To facilitate data locality in multi-region statistics.
Performing a manual failover involves changing the current write region to a different region.
Steps to Perform Manual Failover
Manual failover in Azure Cosmos DB follows these straightforward steps:
-
Locate the Cosmos DB Account
: Visit the Azure portal, navigate to the Cosmos DB service, and select the required Cosmos DB account.
-
Access Features
: In the Cosmos DB account page, select “Replicate Data Globally” from the navigation pane.
-
Choose the New Write Region
: This page displays all the current write and read regions. Perform the manual failover by hovering over the region you want to make the new write region, click on the “…” and choose “Failover”.
-
Confirmation
: Confirm the failover operation. Azure will then reconfigure the system to set the selected region as the new write region. The process happens online and doesn’t cause downtime.
Note: Manual failover is only available for single-master accounts.
Impact of Manual Failover
During failover:
- All the in-flight requests in the current write region are retroactively aborted, resulting in immediate consistency.
- Read operations are not influenced and continue as usual.
- Write operations are queued during failover and are committed once the new write region is confirmed.
Remember, while the manual failover process incurs virtually zero downtime, it may take some moments for the system to adjust to the new configuration.
Conclusion
The capability to execute manual failovers, therefore, empowers developers to manage data distribution in case of regional disasters actively. It also permits optimizing Cosmos DB performance by moving the write operations closer to the predominating user load. When preparing for the DP-420 exam, understanding this feature will strengthen your capacity to design resilient Azure Cosmos DB implementations.
Practice Test
True or False: Moving single master write regions requires a forced failover in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Forced failovers are used to move single master write regions. They disrupt continuity but help in moving the write region to the desired location.
Which command is used to initiate a manual failover in Azure Cosmos DB?
- a) FailoverGroups.ReplicaFailover
- b) DatabaseAccounts.FailoverPriorityChange
- c) CosmosDBAccounts.FailoverPriorityChange
- d) None of the above
Answer: b) DatabaseAccounts.FailoverPriorityChange
Explanation: The DatabaseAccounts.FailoverPriorityChange command is used to initiate a manual failover in Azure Cosmos DB.
True or False: Automatic failovers are recommended to move single master write regions in Azure Cosmos DB.
- True
- False
Answer: False
Explanation: Manual failovers, not automatic, are recommended to move single master write regions in Azure Cosmos DB.
The manual failover in Azure Cosmos DB is a __________ activity.
- a) read path
- b) write path
- c) both read and write path
- d) None of the above
Answer: b) write path
Explanation: The manual failover only affects the write availability, hence it is a write path activity.
Can you perform a manual failover in Azure Cosmos DB using Azure Portal?
- a) Yes
- b) No
Answer: a) Yes
Explanation: Manual failover in Azure Cosmos DB can be initiated from Azure Portal, Azure CLI, or Azure PowerShell.
Manual failover in Azure Cosmos DB can cause data loss.
- a) True
- b) False
Answer: b) False
Explanation: Azure Cosmos DB’s multi-master mode provides multiple write regions and replication with no data loss.
What should be the failover policy configuration to induce a planned manual failover without data loss?
- a) Read all Writes
- b) Write all Reads
- c) Eventual consistency
- d) Consistent Prefix
Answer: a) Read all Writes
Explanation: The failover policy should be set to Read all Writes to ensure a planned manual failover without data loss.
True or False: During a manual failover in Azure Cosmos DB, the read regions can remain unaffected.
- True
- False
Answer: True
Explanation: During a manual failover, only the write region is affected. The read regions can continue serving traffic and stay unaffected.
What purpose does performing manual failovers to move single master write regions serve in Azure Cosmos DB?
- a) It helps manage data distribution.
- b) It helps redirect traffic to desired locations.
- c) It helps test failover strategies.
- d) All of the above.
Answer: d) All of the above.
Explanation: Manual failovers manage data distribution, redirect traffic, and are a crucial part of testing failover strategies.
You need to shut down the Cosmos DB service to perform a manual failover.
- a) True
- b) False
Answer: b) False
Explanation: Azure Cosmos DB’s manual failover operation does not require a shut down of the service.
Interview Questions
What is the purpose of performing manual failovers in Microsoft Azure Cosmos DB?
Manual failovers in Azure Cosmos DB allow users to stress-test their application and ensure it responds appropriately during regional failures. It aids in moving the single-master write regions to explore Cosmos DB’s global distribution features and to rearrange regions as per the application’s demand.
What is a region in terms of Azure Cosmos DB?
A region in Azure Cosmos DB is defined as a specified geographical location in which your Azure Cosmos DB data is hosted and is used to reduce latency in application services.
What does the term ‘write region’ mean in Azure Cosmos DB?
In Azure Cosmos DB, the ‘write region’ refers to the region where all the write operations are performed when using single-master mode.
What happens if Azure Cosmos DB’s write region has a total outage?
If an Azure Cosmos DB write region suffers a complete outage, services will automatically failover to the secondary (read) region, converting it into the write region to maintain data availability.
How many write regions do a single-master mode Azure Cosmos DB account have?
A single-master mode Azure Cosmos DB account has only one write region. However, it can have multiple read regions.
Is automatic failover supported in Azure Cosmos DB?
Yes, Azure Cosmos DB supports automatic failover. If the current write region is unavailable, Azure Cosmos DB will automatically promote a read region to be the new write region.
How can you perform a manual failover in Azure Cosmos DB?
A manual failover can be performed in the Azure portal, through Azure CLI, PowerShell, or the Azure Cosmos DB .NET SDK. In the Azure portal, manual failover is performed by rearranging the priority order of regions under the ‘Global Distribution’ setting in your Cosmos DB account.
Can you perform a manual failover on an Azure Cosmos DB account configured with multiple write regions?
No, manual failover is not possible with accounts configured with multiple write regions. The manual failover option is only available for accounts with a single write region.
What steps should be taken before performing a manual failover in Azure Cosmos DB?
Before performing a manual failover, it’s first recommended to perform thorough testing in a pre-production or staging environment. Users must also ensure their application is designed to handle the effects of a failover.
How long does a manual failover take in Azure Cosmos DB?
The duration of a manual failover depends on the size of the database and the current operational throughput but usually, it takes a few seconds to several minutes.
Does the execution of a manual failover cause any interruption of service?
While Azure Cosmos DB is designed to handle failovers smoothly, some minimal interruptions may be experienced during the process, depending on the application configuration and latency sensitivity.
How can you determine when the failover operation is complete?
You can monitor the progress of the failover in Azure portal’s notifications. Once the operation is complete, the portal will display a message confirming the same.
Can I cancel a manual failover operation once the process has begun?
No, once a manual failover operation has started, it cannot be canceled.
How is data consistency maintained during a failover in Azure Cosmos DB?
Azure Cosmos DB maintains data consistency during a failover based on the consistency level (such as Eventual, Session, Bounded staleness, Consistent prefix, or Strong) set in the Cosmos DB operations.
Does Azure Cosmos DB offer any SLA (Service Level Agreement) regarding failover capabilities?
Yes, Azure Cosmos DB does have an SLA, promising high availability with multi-homing capabilities and automatic and manual failover options.
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