设计灾难恢复系统

System requirements

For the scope of our problem, we will only consider the following resources in our architecture,

• Virtual machines
• Web servers
• Databases
• Virtual networks
• Traffic Manager
• Load balancer
• Analytics database.

Functional:

1. Data Backup:
2. The system should automatically back up virtual machines, web servers, databases, virtual networks, and analytics databases on a regular basis.
3. It should support various backup types such as full backups, incremental backups, and differential backups.
4. It should ensure that backups are stored securely and offsite to prevent data loss in case of on-premises disasters.
5. System Replication:
6. The system should replicate virtual machines, web servers, and databases in real-time or near-real-time to ensure redundancy.
7. It should utilize synchronous or asynchronous replication depending on the recovery objectives and latency tolerance.
8. It should replicate data across geographically diverse locations to mitigate regional disasters.
9. Failover Procedures:
10. The system should accept failover rules and procedures to automatically switch traffic from primary systems to redundant systems in case of a disaster.
11. It should ensure failover is seamless and transparent to end-users to minimize downtime.
12. Risk Assessment:
13. The user should conduct regular risk assessments to identify potential threats and vulnerabilities to the IT systems.
14. User should assess the impact of each risk on critical assets and prioritize them accordingly.
15. Identify Critical Assets:
16. The system should identify critical virtual machines, web servers, databases, and analytics databases that are essential for business operations.
17. It should classify assets based on their importance and criticality to prioritize recovery efforts.
18. Define Recovery Objectives:
19. It should define recovery time objectives (RTOs) and recovery point objectives (RPOs) for each critical asset.
20. It should ensure RTOs and RPOs align with business requirements and acceptable levels of downtime and data loss.

Non-Functional:

1. Performance:
2. Ensure minimal impact on system performance during data backup, replication, and failover operations.
3. Define performance metrics and thresholds to monitor system performance and ensure it meets acceptable levels.
4. Scalability:
5. Design the disaster recovery system to scale seamlessly as the organization grows and as data volumes increase.
6. Ensure scalability across virtual machines, web servers, databases, and other components to accommodate future growth.
7. Reliability:
8. Ensure high reliability of the disaster recovery system to minimize the risk of failures or downtime.
9. Implement redundancy and fault-tolerant mechanisms to ensure system availability even in the event of component failures.
10. Security:
11. Implement robust security measures to protect data during backup, replication, and failover processes.
12. Ensure data encryption, access controls, and secure transmission protocols are in place to prevent unauthorized access or data breaches.
13. Compliance:
14. Ensure compliance with relevant regulations and industry standards for data protection and disaster recovery.
15. Regularly audit the disaster recovery system to ensure compliance with regulatory requirements.

Capacity estimation

For capacity estimation we need to consider that our internal components like Database Backup Component, VM-Disk Backup Component should be able to take backups and snapshots efficiently even when the number of database copies and vm-disks increase in number.

let us consider a system where we have 100 Virtual machines, 2 VM disks, that is 200 VM-disks total, 100 database servers in each region. So our systems should be able to handle replication and do backup for the above systems within reasonable times.

Replication

• For Virtual machines and databases which are classified under High Change Rate Environment, we will need to have a Continuous Data Protection (CDP) with Near-Real-Time Replication (e.g., Every 15 Minutes)
• For Moderate Change Rate Environment : Replication Frequency is every few hours (e.g., 4-6 Hours)
• Low Change Rate Environments replication frequency is Daily to Weekly

Backup

• For Virtual machines and databases which are classified under High Change Rate Environment, we will need to have a backup hourly to every few hours
• For Moderate Change Rate Environment : Backup Frequency is Daily
• Low Change Rate Environments replication frequency is Daily or Weekly

Backup Retention

• Critical Systems with Stringent RPO and RTO Requirements:
• Continuous Data Protection (CDP): Retain backups for 30 days to 1 year.
• Retention Period for Full Backups: 7 to 30 days.
• Retention Period for Incremental or Differential Backups: 24 to 72 hours.
• Non-Critical Systems or Historical Data:
• Weekly or Monthly Backups: Retain backups for 1 to 5 years.
• Retention Period for Full Backups: 30 days to 5 years.
• Retention Period for Incremental or Differential Backups: 7 to 30 days.

API design

Below are a few API's we would need for our system, these are not exhaustive lists but some of the most essential ones.

Backup API's

1. Create Full Backup API:
2. Description: This API allows the system to initiate the creation of a full backup for specified resources such as virtual machines, databases, or entire systems. It triggers the backup process to capture the current state of the resource and save it as a complete backup image.
3. Get List of Backups API:
4. Description: This API retrieves a list of available backups for a given resource or set of resources. It provides metadata and information about each backup, such as timestamps, versions, and sizes, enabling administrators to manage and select backups for recovery purposes.
5. Apply Backup Image API:
6. Description: This API facilitates the restoration of resources from a backup image. It allows the system to apply a selected backup image to the corresponding resource, restoring it to a previous state. This process may involve restoring virtual machines, databases, or other components from the backup data.

Replication API's

1. Start Replication API:
2. Description: This API initiates the replication process for specified resources, such as virtual machines or databases. It triggers the creation of replicated copies of the resources to ensure redundancy and availability.
3. Pause Replication API:
4. Description: This API temporarily halts the replication process for specified resources. It allows administrators to pause replication operations for maintenance tasks or to address performance issues without disrupting ongoing replication.
5. Resume Replication API:
6. Description: This API resumes the replication process for resources that were previously paused. It reactivates replication operations, allowing data to continue syncing between primary and secondary locations.
7. Get Replication Status API:
8. Description: This API retrieves the current status of replication for specified resources. It provides information about replication progress, replication lag, and any errors or issues encountered during the replication process.
9. Configure Replication Settings API:
10. Description: This API allows administrators to configure replication settings for specified resources. It includes parameters such as replication frequency, replication method (e.g., synchronous or asynchronous), and target replication location.
11. Failover Trigger API:
12. Description: This API initiates the failover process for resources in the event of a disaster or planned maintenance. It triggers the switchover from primary to secondary resources to ensure continuous availability and data access.
13. Failback Trigger API:
14. Description: This API initiates the failback process after a failover event. It facilitates the return of operations to the primary resources once they are restored and operational again, ensuring a seamless transition back to normal operations.

Database design

Defining the system data model early on will clarify how data will flow among different components of the system. Also you could draw an ER diagram using the diagramming tool to enhance your design...

High-level design

Below are the components which will be require to support the disaster recovery system.

1. Database Backup Component:
2. Responsible for backing up databases regularly to ensure data protection.
3. Utilizes database-native backup mechanisms or backup agents to capture database backups.
4. Coordinates backup schedules and policies based on RPO requirements.
5. VM-Disk Backup Component:
6. Handles the backup of VM disks, including operating system and application data.
7. Utilizes hypervisor-based snapshots or backup agents installed within VMs for disk-level backups.
8. Supports incremental backups and deduplication to minimize backup storage requirements.
9. Smart Load Balancer:
10. Distributes incoming traffic across multiple backend servers or instances to optimize performance.
11. Monitors server health and dynamically adjusts traffic routing based on predefined policies.
12. Integrates with health monitoring and alerting systems to detect and respond to server failures.
13. Traffic Router:
14. Routes incoming traffic to appropriate destinations based on predefined rules and policies.
15. Utilizes DNS-based load balancing and failover mechanisms for traffic redirection.
16. Supports global server load balancing (GSLB) for optimizing traffic distribution across multiple data centers or cloud regions.
17. Configuration Store Database:
18. Stores configuration data and settings for the disaster recovery system components.
19. Provides a centralized repository for managing configuration changes and updates.
20. Cold Storage Database:
21. Stores backup data in a secure and cost-effective manner for long-term retention.
22. Utilizes storage technologies optimized for infrequently accessed data, such as object storage or archival storage services.
23. Secure Vault:
24. Stores sensitive information such as secrets, certificates, and encryption keys used by the disaster recovery system.
25. Implements strong access controls and encryption to protect sensitive data from unauthorized access.
26. Monitoring Service and Database:
27. Monitors the health and performance of the disaster recovery system components.
28. Collects and analyzes metrics, logs, and events to detect anomalies and performance issues.
29. Stores monitoring data in a centralized database for analysis and reporting.
30. Alerting or Notification Database:
31. Stores alerting and notification configurations, rules, and policies.
32. Generates alerts and notifications based on predefined thresholds and conditions.
33. Integrates with external notification services to notify stakeholders of critical events and incidents.
34. Configuration Service:
35. Provides a centralized platform for managing configuration settings and parameters for all components of the disaster recovery system.
36. Allows administrators to define and update configuration settings for individual components or groups of components.
37. Supports versioning and change tracking to ensure accountability and auditability of configuration changes.

Request flows

Explain how the request flows from end to end in your high level design. Also you could draw a sequence diagram using the diagramming tool to enhance your explanation...

Detailed component design

When customers are considering disaster recovery for their systems, there are several key decisions they need to make to ensure an effective and resilient solution. These decisions will serve either as configurations to the backup and replication system or guidelines when the customer is trying to simulate a disaster recovery drill Some of these decisions include:

• Recovery Time Objective (RTO) and Recovery Point Objective (RPO):
• Customers must define the acceptable downtime (RTO) and data loss (RPO) tolerances for their systems.
• This helps determine the level of redundancy, replication frequency, and failover mechanisms needed.
• Data Replication Strategy:
• Choose between synchronous or asynchronous replication based on their business requirements, network bandwidth, and data consistency needs.
• Synchronous replication offers real-time data consistency but may impact performance.
• Asynchronous replication provides flexibility with potential data loss.
• Geographical Redundancy:
• Customers must decide whether to replicate data within the same region (Locally Redundant Storage - LRS) or across multiple regions (Zone Redundant Storage - ZRS) to ensure geographic redundancy and mitigate risks associated with regional disasters.
• Backup Retention and Storage:
• Customers must determine backup retention policies, including the frequency of backups and the duration for which backup data should be retained. This decision must be taken for all different components depending on criticality of the component.
• Choose appropriate storage solutions based on durability, availability, and cost considerations.
• Failover Strategy:
• Define failover procedures and mechanisms to ensure seamless transition from primary to secondary systems in the event of a disaster.
• This may involve configuring automatic failover, setting up traffic routing policies, and conducting failover drills.
• Capacity Planning and Resource Reservation:
• Estimate the capacity requirements for secondary systems, including compute, storage, and networking resources.
• Reserve capacity in advance to accommodate failover scenarios and ensure sufficient resources are available when needed.
• Compliance and Security:
• Consider regulatory compliance requirements and security considerations when designing the disaster recovery solution. Ensure that data protection measures, encryption standards, and access controls are in place to safeguard sensitive information.
• Testing and Maintenance:
• Establish procedures for testing the disaster recovery system regularly to verify its effectiveness and identify any potential issues or gaps. Schedule routine maintenance tasks, such as software updates and security patches, to keep the system resilient and up-to-date.

Backup component

let us now discuss the backup component, for this component we will discuss some components which are a part of internal architecture and we will also discuss what should be supported by the backup components.

Internal components

The internal architecture of the backup component typically consists of several modules or layers that work together to facilitate data backup, storage, and recovery. Here's an expanded overview of the internal architecture:

1. User Interface (UI):
2. Provides a graphical or command-line interface for administrators to configure backup policies, monitor backup jobs, and manage backup storage.
3. Allows users to initiate backup and restore operations, schedule backup jobs, and view backup reports.
4. Backup Scheduler:
5. Responsible for scheduling backup jobs based on predefined backup policies and schedules.
6. Coordinates the execution of backup tasks, ensuring that backups are performed at specified intervals and times.
7. Backup Engine:
8. Core component responsible for performing backup operations.
9. Implements backup methods such as full backups, incremental backups, and differential backups.
10. Manages data deduplication, compression, and encryption to optimize backup storage and security.
11. Backup Agents:
12. Installed on servers, virtual machines, or endpoints to facilitate backup operations at the source.
13. Responsible for capturing and transmitting data to the backup server or storage repository.
14. Provides functionality for application-aware backups, ensuring consistency and integrity of application data.
15. Backup Repository:
16. Stores backup data in a secure and scalable manner.
17. Includes disk-based storage, tape libraries, or cloud storage solutions.
18. Supports features such as versioning, retention policies, and data deduplication.
19. Backups are usually stored in backup vaults which are specially designed to store the backups.
20. Metadata Store:
21. Stores metadata associated with backup jobs, such as backup timestamps, file attributes, and backup chain relationships.
22. Enables efficient cataloging and indexing of backup data for quick retrieval and recovery.
23. Encryption and Compression:
24. Implements encryption algorithms to secure backup data both in transit and at rest.
25. Performs data compression to reduce storage requirements and optimize backup performance.
26. Monitoring and Reporting:
27. Monitors backup job status, storage utilization, and system performance.
28. Generates alerts for backup failures, storage capacity issues, and other critical events.
29. Generates reports and dashboards to provide insights into backup activities, compliance status, and resource utilization.

Backup component design consideration

Below are the design considerations that need to be kept in mind while designing the backup component. These following points tell us about the features and the scale requirements of the component.

1. Backup Types:
2. Full Backup: Takes a complete copy of the data.
3. Incremental Backup: Captures changes made since the last backup.
4. Differential Backup: Captures changes made since the last full backup.
5. Backup Frequency:
6. Define backup schedules based on the criticality of data and business requirements.
7. Consider factors like data volatility and RPOs when determining backup frequency.
8. Backup Methods:
9. Snapshot-based Backup: Utilizes storage snapshots to capture the state of data at a specific point in time.
10. Agent-based Backup: Installs backup agents on servers to facilitate backup operations.
11. Cloud-native Backup: Leverages cloud provider tools and APIs for backup operations.
12. Backup Storage:
13. Determine storage requirements based on data volume, retention policies, and compliance regulations.
14. Choose between on-premises storage, cloud storage, or a hybrid approach.
15. Consider factors like scalability, durability, and cost-effectiveness when selecting storage solutions.
16. Encryption and Security:
17. Implement encryption mechanisms to secure backup data both in transit and at rest.
18. Ensure compliance with security standards and regulations.
19. Implement access controls and authentication mechanisms to restrict access to backup data.
20. Monitoring and Reporting:
21. Implement monitoring tools to track backup jobs, storage usage, and backup performance.
22. Set up alerts for backup failures, storage capacity issues, and other critical events.
23. Generate regular reports to assess backup effectiveness, compliance, and resource utilization.
24. Scalability and Flexibility:
25. Design backup solutions that can scale with growing data volumes and infrastructure requirements.
26. Consider future expansion and technology advancements when designing backup architectures.
27. Disaster Recovery Integration:
28. Ensure compatibility with disaster recovery solutions for seamless failover and data recovery.
29. Coordinate backup and replication strategies to meet RPOs and RTOs for disaster recovery scenarios.

Backup Component and Recovery Point Objective (RPO):

• RPO refers to the maximum acceptable amount of data loss that an organization can tolerate during a disruption or disaster.
• It defines the point in time to which data must be recovered after an incident.
• The backup component plays a crucial role in meeting RPO requirements by ensuring that backup intervals are frequent enough to capture changes to data within the defined RPO timeframe. For example, if the RPO is one hour, backups should be taken at least every hour to minimize data loss.

Replication Component

The Replication component forms a critical aspect of disaster recovery systems, ensuring the continuous synchronization of data between primary and secondary sites. By replicating data in real-time or with defined intervals, it aims to minimize data loss and maintain business continuity in the event of a disaster. Through careful design considerations and robust internal architecture, the Replication component plays a pivotal role in achieving high availability, data consistency, and rapid failover capabilities within organizations.

Design Considerations for Replication Component:

1. Replication Types:
2. Synchronous Replication: Ensures that data is mirrored to the target location in real-time, guaranteeing data consistency but potentially impacting performance.
3. Asynchronous Replication: Allows for a delay between data writes and replication, providing flexibility in balancing performance and consistency.
4. Topology:
5. Active-Passive: One primary site actively serves traffic while the secondary site remains passive for failover purposes.
6. Active-Active: Both primary and secondary sites actively serve traffic, providing load balancing and high availability.
7. Network Bandwidth:
8. Determine the required network bandwidth for replication traffic based on data volume, replication frequency, and distance between sites.
9. Implement compression and deduplication techniques to optimize bandwidth usage.
10. Data Consistency:
11. Ensure data consistency between primary and secondary sites to avoid inconsistencies and data corruption.
12. Implement mechanisms such as write-order fidelity and consistency groups to maintain data integrity during replication.
13. Failover Mechanism:
14. Define failover procedures and mechanisms to ensure seamless failover from the primary site to the secondary site in case of a disaster or outage.
15. Implement health checks and monitoring to automatically initiate failover when necessary.
16. Recovery Point Objective (RPO):
17. Ensure that the replication frequency aligns with the organization's RPO requirements to minimize data loss in the event of a disaster.
18. Recovery Time Objective (RTO):
19. Design the replication component to support fast and efficient failover processes, minimizing downtime and meeting RTO objectives.

Internal Architecture of Replication Component:

1. Replication Engine:
2. Core component responsible for data replication between primary and secondary sites.
3. Implements replication protocols and algorithms to efficiently synchronize data changes.
4. Replication Agents:
5. Deployed on primary and secondary servers to capture and transmit data changes to the replication engine.
6. Ensure that data consistency and integrity are maintained during replication.
7. Replication Channels:
8. Communication channels used for transmitting replicated data between primary and secondary sites.
9. Utilize network protocols such as TCP/IP or specialized replication protocols for efficient data transfer.
10. Conflict Resolution Mechanisms:
11. Handle conflicts that may arise when the same data is modified concurrently on both primary and secondary sites.
12. Implement conflict resolution policies to resolve conflicts and maintain data consistency.
13. Checkpointing and Resynchronization:
14. Maintain checkpoints to track the replication progress and ensure data consistency.
15. Support resynchronization mechanisms to recover from replication failures and discrepancies.
16. Monitoring and Management:
17. Monitor replication status, latency, and throughput to ensure replication health and performance.
18. Provide management interfaces for configuring replication settings, monitoring replication progress, and troubleshooting issues.
19. Security and Authentication:
20. Implement encryption and authentication mechanisms to secure replication traffic and prevent unauthorized access.
21. Ensure compliance with data protection regulations and industry standards.

Replication Component and RTO (Recovery Time Objective)

The RTO (Recovery Time Objective) is closely related to the Replication component within disaster recovery systems. RTO refers to the maximum acceptable downtime allowed for restoring systems and services after a disruption or disaster.

The Replication component directly impacts RTO by facilitating rapid failover and data recovery processes. By continuously synchronizing data between primary and secondary sites, replication ensures that a standby environment is kept up-to-date with the latest data changes. In the event of a disaster or outage at the primary site, the replicated data can be quickly activated at the secondary site, reducing the time needed to restore services and minimizing downtime.

Disaster Recovery System

Combining the backup and replication components forms a comprehensive disaster recovery system that ensures data protection, business continuity, and rapid recovery capabilities. Here's how the two components can be integrated to create an effective disaster recovery solution:

1. Data Protection and Redundancy:
2. Utilize the backup component to regularly capture and store copies of critical data and systems. This ensures data redundancy and provides a fallback in case of data loss or corruption.
3. Employ the replication component to mirror data in real-time or with defined intervals between primary and secondary sites. This maintains synchronized copies of data, offering redundancy and minimizing data loss.
4. Rapid Recovery and Failover:
5. Leverage the replication component for rapid failover in the event of a disaster or outage at the primary site. The synchronized data at the secondary site can be quickly activated to restore services, minimizing downtime and meeting RTO objectives.
6. Combine backup data with replication for additional recovery options. In scenarios where the primary site becomes inaccessible or data becomes corrupted, backup copies can be used alongside replicated data to facilitate recovery and restore operations swiftly.
7. Flexible Recovery Options:
8. Integrate backup and replication strategies to offer flexible recovery options based on the nature and severity of the disaster. Depending on the situation, organizations can choose to recover from backups, replicated data, or a combination of both.
9. Implement tiered recovery strategies to prioritize critical systems and data for rapid restoration, while less critical data can be recovered from backups with longer RTOs.
10. Testing and Validation:
11. Conduct regular testing and validation of backup and replication processes to ensure their effectiveness in real-world disaster scenarios. Perform disaster recovery drills and simulations to assess the system's ability to meet recovery objectives and identify areas for improvement.
12. Monitoring and Management:
13. Implement monitoring and management tools to track the status of backup and replication jobs, monitor replication health, and detect any anomalies or failures.
14. Set up alerts and notifications to promptly notify administrators of backup failures, replication lag, or other issues that may impact the disaster recovery system's performance.

Trade offs/Tech choices

Explain any trade offs you have made and why you made certain tech choices...

Failure scenarios/bottlenecks

Try to discuss as many failure scenarios/bottlenecks as possible.

Future improvements

What are some future improvements you would make? How would you mitigate the failure scenario(s) you described above?