A crucial part of this certification exam, indeed one of the most critical concepts, is defining automatic failover policies for regional failure for Azure Cosmos DB in the context of NoSQL. It is paramount to understand this concept thoroughly, so let’s break it down for the perfect understanding.
Automatic Failover Policies in Azure Cosmos DB
Azure Cosmos DB provides multi-region replication to ensure high availability. One of the scenarios it covers is to mitigate the impact of a regional failure. To handle these failures, Azure Cosmos DB employs Automatic Failover Policies.
These policies facilitate a failover to another region in case the primary region of Azure Cosmos DB account becomes unavailable due to regional failure, such as natural disasters. The failover will cause minimum disruption of service to the end-users.
Let’s look at an example of this. Imagine you have an Azure Cosmos DB based application that is attached to three different regions: East Asia (primary), North Europe, and West US. In the case that East Asia experiences a failure, automatic failover will initiate, changing the primary read region to North Europe (if it is the second on your priority list).
Defining Automatic Failover Policies
Here’s how to set up the automatic failover priority:
In the Azure portal, navigate to your Azure Cosmos DB account.
- Select ‘Replicate data globally’ under the ‘Settings’ section.
- On the ‘Global Distribution’ blade which opens, ensure that automatic-failover is enabled.
- Prioritize your regions according to the failover path. The first region in the list is your primary region. In case of a regional failure, Azure Cosmos DB will failover in the sequence of this list.
Note that during a failover process, both read and write traffic is shifted to the replica that is highest on the path priority once the failover has been completed.
Handling Regional Failures
The handling of regional failures is an automatic process governed by Microsoft. However, if needed, a manual failover can also be initiated. This is useful when you want to test the failover process or change the primary region for planned maintenance or other business scenarios.
Please note that after regional failure, when the failed region comes back online, it becomes a secondary replica. The writes and reads no longer get served from this region. You need to initiate the manual failover if you want to make it a primary replica again.
Here is an example of how to trigger a manual failover using Azure CLI:
az cosmosdb failover-priority-change --name MyCosmosDBDatabaseAccount --resource-group MyResourceGroup --failover-policies EastAsia=0 NorthEurope=1 WestUS=2
Keep in mind that the keys represent the regions’ names and the values show the failover priority, with 0 being the highest priority.
Thus, the automatic failover policies for Azure Cosmos DB play a crucial role in maintaining high availability and minimizing the impact of regional failures. As a DP-420 certification aspirant, a complete understanding and the ability to implement such policies are a vital part of the certification journey. Make sure to test your application thoroughly to ensure that the failover process transitions smoothly without massive impacts on in-flight operations.
Practice Test
True or False: Azure Cosmos DB supports automatic failover.
- True
- False
Answer: True
Explanation: Azure Cosmos DB offers automatic and manual failover features. This ensures that your data is always available in case of a regional outage.
True or False: In the event of a regional failure, Azure Cosmos DB will automatically replicate data to all regions.
- True
- False
Answer: True
Explanation: Azure Cosmos DB ensures high availability by automatically replicating data to all regions of its global distribution.
Which of the following are benefits of automatic failover in Azure Cosmos DB? (Select all that apply)
- a) Increased availability
- b) Improved write latency
- c) Reduced manual intervention
- d) Limited regional control
Answer: a, b, c
Explanation: Automatic failover increases the availability of your data, improves write latency by allowing writes to occur in multiple regions, and reduces the need for manual intervention during a regional outage.
True or False: Azure Cosmos DB allows you to set a preferred region for data replication during a failover event?
- True
- False
Answer: True
Explanation: Azure Cosmos DB does provide the feature where you can define a preferred list of regions for failover to ensure the data is accessible during regional outage.
What is the maximum delay for data replication in Azure Cosmos DB during a regional failure?
- a) 5 seconds
- b) 10 seconds
- c) 15 seconds
- d) There is no specified maximum delay
Answer: d
Explanation: Azure Cosmos DB does not specify a maximum delay for data replication. It uses multi-master replication to ensure that data is replicated across all regions in near real-time.
True or False: Read operations can only be performed in the region where the data was written in Azure Cosmos DB.
- True
- False
Answer: False
Explanation: Due to Azure Cosmos DB’s multi-master replication, read operations can be performed in any region where the data is replicated, not just the original write region.
In Azure Cosmos DB, which of the following is used to control the order of failover objectives in case of a regional outage?
- a) Load balancer
- b) Failover policy
- c) Parallel processing
- d) None of the above
Answer: b
Explanation: In case of a regional outage, Azure Cosmos DB uses a failover policy to control the order of regions for failover.
True or False: You can manually trigger a regional failover in Azure Cosmos DB for testing purposes.
- True
- False
Answer: True
Explanation: Azure Cosmos DB allows you to manually trigger a regional failover for testing purposes without waiting for an actual regional outage.
How many read replicas can you have per region for each Azure Cosmos DB account?
- a) 1
- b) 2
- c) 4
- d) Unlimited
Answer: a
Explanation: Each Azure Cosmos DB account offers a single read replica per region for each database.
True or False: Automatic failover in Azure Cosmos DB works in a round-robin manner.
- True
- False
Answer: False
Explanation: Automatic failover in Azure Cosmos DB works on a failover priority list which is set at the database level, not on a round-robin basis.
Interview Questions
What is Azure Cosmos DB failover policy?
Azure Cosmos DB failover policy is a set and forget policy that allows automatic and manual failover during regional outages to assure business continuity and data availability.
What are the types of failover supported by Azure Cosmos DB?
Azure Cosmos DB supports two types of failovers – automatic and manual. Automatic failover enables Azure to failover to a secondary region in the case of a regional disaster, while manual failover is initiated by users as per their requirement.
What is NoSQL in the context of Azure Cosmos DB?
NoSQL in the context of Azure Cosmos DB is a non-relational database service that allows for flexible data storage and management. It has a horizontally scalable architecture, supports multiple data models including document, key-value, and graph, and enables globally-distributed applications.
What is the function of the priority list in Azure Cosmos DB’s automatic failover policy?
The priority list in Azure Cosmos DB’s automatic failover policy defines the order in which regions will be selected for failover during a regional disaster. The system will failover to the top available region in the list.
How can you configure automatic failover in Azure Cosmos DB?
You can configure automatic failover in Azure Cosmos DB through either the Azure portal or programmatically using Azure Cosmos DB SDKs or REST API. In the Azure portal, you can set it up under the ‘Replicate data globally’ section of your Cosmos DB account.
What does RPO stand for in the context of Azure Cosmos DB and how is it significant for regional failure?
RPO stands for Recovery Point Objective and highlights the acceptable amount of data loss measured in time. When a regional failure happens, Azure Cosmos DB uses RPO to determine how much data can be lost in the process.
What does RTO stand for in the context of Azure Cosmos DB and how is it significant for regional failure?
RTO stands for Recovery Time Objective and represents the acceptable amount of time it takes to restore service after a failure. In the context of a regional failure, Azure Cosmos DB aims to meet this objective to ensure minimal disruption.
Are all Azure Cosmos DB features available during a regional failure?
During a regional failure, writes are not permitted until the failover is complete and the region has recovered. However, reads can be served from other available regions if multi-region replication is enabled.
Can you reorder regions in the Cosmos DB priority list after setting them?
Yes, you can reorder the regions in the Azure Cosmos DB priority list at any time to meet the changing requirements of your business.
How many secondary regions can you add to Azure Cosmos DB for automatic failover?
You can add up to nine (9) secondary regions to Azure Cosmos DB for automatic failover, ensuring that your application remains highly available even during a regional failure.
What role does Azure Cosmos DB’s multi-region feature play in case of a regional failure?
Azure Cosmos DB’s multi-region feature supports automatic and manual failovers and provides low-latency access to data from any region. This ensures that during a regional failure, the impact on the service is minimized.
How does Azure Cosmos DB guarantee data durability in case of a regional failure?
Azure Cosmos DB employs a multi-region write capability to ensure data durability. By distributing data across multiple regions, even if a primary region fails, the data is still available at other regions, ensuring no data loss.
How is consistency achieved in Azure Cosmos DB during a regional failure?
Azure Cosmos DB provides multiple consistency models including immediate, session, bounded staleness, consistent prefix, and eventual, which customers can select based on their requirement – delivering a flexible and reliable performance even during a regional failure.
What happens if the primary region of Azure Cosmos DB has a failure?
If the primary region of Azure Cosmos DB experiences a failure, the service automatically triggers a failover to a secondary region from the priority list, ensuring that the application continues to run with minimal disruption.
Can I do a manual failover while an automatic failover is underway in Azure Cosmos DB?
No, a manual failover cannot be performed during an automatic failover in Azure Cosmos DB as it could potentially disrupt the system and lead to unnecessary complications.
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