Conceptually, a region pertains to a geographical location on the globe where Azure Cosmos DB sends and retrieves data. Specifying a region for global distribution is an essential aspect of designing and implementing native applications using Microsoft’s Azure Cosmos DB, given that it influences the overall performance and availability of an application.
Specifying a region for worldwide distribution fundamentally concerns two major concepts: one is replication, and the second is regional failover.
Replication
One of the features of Azure Cosmos DB is the automatic replication of data across multiple Azure regions. This means that once you add a region, Azure Cosmos DB will automatically replicate your data to that region. Moreover, the write region can also be switched seamlessly without any downtime.
Consider the scenario where we have a Cosmos DB account named ‘CosmosDBAccount1’, and want to add ‘West US’ as a new region. The Azure CLI command would be as follows:
az cosmosdb failover-priority-change –resource-group MyResourceGroup –name CosmosDBAccount1 –failover-policies West US=0 East US=1
This command adds ‘West US’ as a new region with failover priority 0, making it the new write region, and ‘East US’ is now the secondary read region with failover priority 1.
Regional Failover
Azure Cosmos DB automatically handles regional failover in the event of a regional outage. It maintains multiple copies of data and log records in a distributed, durable, and highly available manner. In terms of regional failover, Azure Cosmos DB provides two options:
- Automatic Failover: In the event of a regional outage, Cosmos DB triggers an automatic failover to the next available region in the priority list.
- Manual Failover: You can also trigger a failover manually, moving the workload to another region without experiencing any downtime during the failover process.
To illustrate manual failover with PowerShell, consider the following example:
$failoverPolicies = @()
$failoverPolicies += New-CosmosDbAccountFailoverPolicy -LocationName “West US” -FailoverPriority 0
$failoverPolicies += New-CosmosDbAccountFailoverPolicy -LocationName “East US” -FailoverPriority 1
Set-CosmosDbAccountFailoverPriority -Name “CosmosDBAccount1” -ResourceGroupName “MyResourceGroup” -FailoverPolicy $failoverPolicies
In the script above, we manually change the failover priority, making ‘West US’ the new write region.
Conclusion
To summarize, specifying a region for global distribution influences the performance, availability, and latency of our Cosmos DB and, by extension, applications. Use of Azure CLI and PowerShell can significantly simplify setting up replication and managing regional failover for Cosmos DB. It is, therefore, crucial for anyone undertaking the DP-420 Designing and Implementing Native Applications Using Microsoft Azure Cosmos DB exam to deeply understand these concepts.
Practice Test
You need to specify a region for global distribution whenever you provide read and write regions in Azure Cosmos DB.
- True
- False
Answer: True
Explanation: Whenever you provide read and write regions in Azure Cosmos DB, it is mandatory to specify a region for global distribution as it governs the geographical area for distributing data.
Azure Cosmos DB enables you to store data in a specific geographical area for low latency in a read-write model.
- True
- False
Answer: True
Explanation: Azure Cosmos DB provides latency guarantees by allowing data to be stored in a certain geographic region to provide high-throughput, low-latency in a read-write model.
In a globally-distributed Azure Cosmos DB, write regions are generally fewer than read regions.
- True
- False
Answer: False
Explanation: In a globally-distributed Azure Cosmos DB application, you can have multiple read regions but only one write region.
Which of the following factors needs to be considered when specifying a region for global distribution?
- Absorption of regional failures
- Low latency access to data on a global scale
- Cost management
- All of the above
Answer: All of the above
Explanation: These are all key considerations when specifying a region for global distribution in Azure Cosmos DB.
Azure Cosmos DB’s API for MongoDB supports multiple write regions.
- True
- False
Answer: False
Explanation: Azure Cosmos DB’s API for MongoDB does not yet support multiple write regions.
Azure Cosmos DB allows you to have more than one write region.
- True
- False
Answer: True
Explanation: Azure Cosmos DB does allow multiple write regions. However, this feature must be enabled as it’s not turned on by default.
The consistency level in Azure Cosmos DB is maintained by default in a globally-distributed database.
- True
- False
Answer: True
Explanation: The consistency is automatically managed by Azure Cosmos DB in a globally-distributed configuration.
Specifying a region is mandatory for local distribution in Azure Cosmos DB.
- True
- False
Answer: False
Explanation: Specifying a region is only mandatory for global distribution. In local distribution, it’s not necessary to specify a region.
All Azure Cosmos DB APIs support automatic failover.
- True
- False
Answer: False
Explanation: Not all APIs of Azure Cosmos DB – such as Azure Cosmos DB’s API for MongoDB, do not currently support automatic failover.
Azure Cosmos DB allows you to distribute your data globally.
- True
- False
Answer: True
Explanation: Azure Cosmos DB is a globally distributed, multi-model database service that is designed to scale throughput and storage across any number of geographical regions with comprehensive SLAs.
A constant ‘Default consistency level’ globally united, in Cosmos DB, can be overridden on a per-request basis.
- True
- False
Answer: True
Explanation: The ‘Default consistency level’ is a global setting for each Cosmos DB-account, but it can be overridden on a per-request basis.
In Azure Cosmos DB, every region associated with your account is a read region.
- True
- False
Answer: True
Explanation: By default, all regions associated with your Cosmos DB account are readable. You can also make any of these regions writable by enabling multiple write regions.
Single-region accounts are not allowed in Cosmos DB for better scalability.
- True
- False
Answer: False
Explanation: Single region accounts are allowed in Cosmos DB and are the simplest configuration. There are different scenarios where they could be the way to go, like when latency is not an issue or cost is a constraint.
It’s not possible to add or remove Azure Cosmos DB regions from the Azure portal.
- True
- False
Answer: False
Explanation: You can add or remove Azure Cosmos DB regions from the Azure portal to manage global data distribution.
Configuring a multi-region account of Cosmos DB not only helps in distributing data but also makes the system resilient to regional failures.
- True
- False
Answer: True
Explanation: Yes, a multi-region configuration provides both, low latency data access, and high availability, even in the event of regional failures.
Interview Questions
What is the main consideration when you specify a region for global distribution in Microsoft Azure Cosmos DB?
The main consideration when defining a region for global distribution is the proximity to the users because it directly affects the latency of your application. The closer your data is to your users, the lower the latency they experience.
How can Microsoft Azure Cosmos DB ensure data latency?
Azure Cosmos DB allows you to replicate your data globally, therefore you can position your data close to your users, minimizing possible data latency.
Why is there a need to specify a region for global distribution in Azure Cosmos DB?
Specifying a region for global distribution allows you to distribute your data globally. This is beneficial to improve the latency and availability of your application.
How does global distribution work in Azure Cosmos DB?
With Azure Cosmos DB, you can distribute your data across different regions around the world. Azure Cosmos DB transparently replicates your data and makes it available close to where the users are.
What is the benefit of enabling multi-region writes in Azure Cosmos DB?
Enabling multi-region writes increases data availability and durability because it allows writing data into several regions, instead of a single write region.
What is a conflict in the context of global distribution in Azure Cosmos DB?
A conflict happens when two or more operations modify the same document concurrently in different regions. Azure Cosmos DB has its own conflict resolution policy which can be configured as per our requirement.
How can conflicts be managed in Azure Cosmos DB?
Cosmos DB provides automatic and custom conflict resolution methods. Automatic conflict resolution provides a “last writer wins” policy. Custom conflict resolution allows you to use stored procedures for conflict handling.
Is it possible to add or remove regions from my Azure Cosmos DB account?
Yes, Azure Cosmos DB allows you to add or remove regions whenever you need it. This flexibility allows you to adapt to changes in the geographical distribution of your users.
What is the maximum number of regions that you can associate with an Azure Cosmos DB account?
The maximum number of regions you can associate with an Azure Cosmos DB account is 30.
How does Azure Cosmos DB achieve high availability?
Azure Cosmos DB uses multi-homing API, which ensures high availability by reshuffling the traffic to the available regions automatically in case of regional outages or disasters.
What does the term “multi-homing” refer to in Azure Cosmos DB?
Multi-homing refers to an Azure Cosmos DB feature which ensures that your application continues to work in the event of regional failures or disasters without the need for changes in application configurations.
How does Azure Cosmos DB ensure data consistency in a globally distributed environment?
Azure Cosmos DB provides five well-defined consistency models which include Eventual, Consistent Prefix, Session, Bounded staleness, and Strong consistency to ensure a high level of data consistency based on application requirements.
What is the role of Azure Traffic Manager in Azure Cosmos DB?
Azure Traffic Manager is not directly associated with Cosmos DB, rather it is used for DNS level global traffic routing. In case of a regional outage, Traffic Manager can redirect incoming requests to a secondary region automatically.
What is the turnaround time for adding a region to a globally distributed Azure Cosmos DB?
Azure Cosmos DB typically adds a region to your globally-distributed database within an hour.
Does Azure Cosmos DB support cross-region transactions?
Yes, Azure Cosmos DB supports cross-region transactions using stored procedure, triggers, and UDFs where all operations are atomic at the logic level inside these operations.
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