System requirements

Functional Requirements

Core Functionalities:

1. Voter Authentication:
   • Authenticate voters using secure credentials or government-issued IDs.
   • Prevent duplicate voting with one vote per voter per election.
2. Ballot Creation and Distribution:
   • Allow administrators to create and manage ballots for different elections or polls.
   • Distribute ballots securely to eligible voters.
3. Vote Casting:
   • Enable voters to cast votes electronically while ensuring ballot secrecy.
   • Validate votes against election rules (e.g., one vote per voter).
4. Result Tabulation:
   • Aggregate votes securely and provide real-time or post-election results.
   • Support multi-tier tabulation for district, state, and national levels.
5. Auditability:
   • Generate verifiable logs of all voting activities for post-election audits.
   • Provide tamper-evident records to ensure integrity.
6. Voter Notifications:
   • Notify voters about ballot availability and confirmation of vote submission.
7. Multi-Language Support:
   • Provide ballots and system interfaces in multiple languages.
8. Election Management:
   • Allow election officials to configure election details, such as start/end times, candidates, and voting rules.

Non-Functional Requirements

1. Scalability:
   • Support millions of voters simultaneously during high-stakes elections.
   • Handle spikes in traffic as voting deadlines approach.
2. Security:
   • Ensure end-to-end encryption of all votes and voter information.
   • Protect against unauthorized access, tampering, and distributed denial-of-service (DDoS) attacks.
3. Availability:
   • Achieve 99.99% uptime during voting periods to ensure uninterrupted access.
4. Data Privacy:
   • Maintain strict separation of voter identities from their votes to ensure anonymity.
5. Auditability:
   • Provide immutable logs for audit purposes while preserving voter privacy.
6. Performance:
   • Ensure low-latency operations for voter authentication and vote casting.
   • Handle result tabulation within seconds to minutes after polls close.
7. Extensibility:
   • Support integration with external government databases and future voting technologies (e.g., blockchain).

Capacity estimation

Estimate the scale of the system you are going to design...

Assumptions:

1. Voters:
   • Total eligible voters: 100 million.
   • Peak simultaneous voters: 10% of total (10 million).
2. Elections:
   • Average active elections at a time: 1,000.
   • Average candidates per election: 10.
3. Vote Casting:
   • Vote size (encrypted): ~1 KB.
   • Total votes during an election: 100M×1 vote=100 million votes100M \times 1 \, \text{vote} = 100 \, \text{million votes}100M×1vote=100million votes.

Resource Estimation:

1. Storage:
   • Total vote data: 100M×1 KB=100 GB100M \times 1 \, \text{KB} = 100 \, \text{GB}100M×1KB=100GB.
   • Logs and audit trails: ~50 GB per election.
2. Bandwidth:
   • Average vote submission: 1 KB.
   • Peak bandwidth: 10M voters×1 KB=10 GB/sec10M \, \text{voters} \times 1 \, \text{KB} = 10 \, \text{GB/sec}10Mvoters×1KB=10GB/sec.
3. Database:
   • Voter database size: 100M×500 bytes/voter=50 GB100M \times 500 \, \text{bytes/voter} = 50 \, \text{GB}100M×500bytes/voter=50GB.
   • Ballot and election metadata: ~5 GB.

API design

Define what APIs are expected from the system...

1. Voter Authentication APIs

• POST /api/auth/login: Authenticate a voter using credentials or government ID.
• POST /api/auth/verify: Verify voter eligibility for an election.

2. Ballot Management APIs

• POST /api/ballots/create: Create a new ballot for an election.
• GET /api/ballots/{election_id}: Retrieve the ballot for a specific election.
• PUT /api/ballots/update/{election_id}: Update ballot details (e.g., candidates).

3. Vote Casting APIs

• POST /api/votes/cast: Submit a vote for an election.
• GET /api/votes/status: Retrieve the status of a submitted vote (e.g., confirmed, pending).

4. Result Tabulation APIs

• GET /api/results/{election_id}: Fetch aggregated results for a specific election.
• GET /api/results/live/{election_id}: Fetch live vote counts during the election.

5. Audit and Logs APIs

• GET /api/audit/logs/{election_id}: Retrieve logs for a specific election.
• POST /api/audit/verify: Verify the integrity of an election using audit trails.

6. Notification APIs

• POST /api/notifications/send: Notify voters of ballot availability or voting confirmation.

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...

1. Voter Database

• Schema Details:
  • Table Name: Voters
    • voter_id (Primary Key): Unique identifier for each voter.
    • name: Full name of the voter.
    • dob: Date of birth.
    • address: Residential address.
    • voting_status: Indicates if the voter has cast a vote.
• Purpose:
  • Store voter details and voting eligibility.
• Tech Used:
  • Relational Database (e.g., PostgreSQL, MySQL).
• Tradeoff:
  • Pros: Ensures strong consistency for voter records.
  • Cons: Requires sharding to handle high query loads during voting.

2. Ballot Database

• Schema Details:
  • Table Name: Ballots
    • election_id (Primary Key): Unique identifier for each election.
    • ballot_data: JSON object containing candidate details and rules.
    • start_time: Voting start time.
    • end_time: Voting end time.
• Purpose:
  • Store ballot definitions and configurations.
• Tech Used:
  • NoSQL Database (e.g., MongoDB).
• Tradeoff:
  • Pros: Flexible schema supports different ballot formats.
  • Cons: Requires additional indexing for complex queries.

3. Votes Database

• Schema Details:
  • Table Name: Votes
    • vote_id (Primary Key): Unique identifier for each vote.
    • election_id (Foreign Key): Associated election ID.
    • voter_id (Foreign Key): Associated voter ID.
    • encrypted_vote: Encrypted vote data.
• Purpose:
  • Store cast votes securely and ensure anonymity.
• Tech Used:
  • Relational Database with encryption (e.g., PostgreSQL with TDE).
• Tradeoff:
  • Pros: Guarantees transactional integrity for vote storage.
  • Cons: Encryption increases query overhead.

4. Audit Logs Database

• Schema Details:
  • Table Name: AuditLogs
    • log_id (Primary Key): Unique identifier for each log entry.
    • election_id (Foreign Key): Associated election ID.
    • action: Type of action logged (e.g., vote cast, voter verified).
    • timestamp: Time of the action.
• Purpose:
  • Track all voting-related activities for auditability.
• Tech Used:
  • Append-only NoSQL Database (e.g., Cassandra).
• Tradeoff:
  • Pros: High write throughput for logging.
  • Cons: Complex queries require additional processing.

5. Notification Database

• Schema Details:
  • Table Name: Notifications
    • notification_id (Primary Key): Unique identifier for each notification.
    • voter_id (Foreign Key): Associated voter ID.
    • message: Notification content.
    • status: Delivery status (e.g., sent, pending).
• Purpose:
  • Track notifications sent to voters.
• Tech Used:
  • NoSQL Database (e.g., DynamoDB).
• Tradeoff:
  • Pros: Scales easily for large notification volumes.
  • Cons: Limited querying capabilities for aggregated reports.

High-level design

You should identify enough components that are needed to solve the actual problem from end to end. Also remember to draw a block diagram using the diagramming tool to augment your design. If you are unfamiliar with the tool, you can simply describe your design to the chat bot and ask it to generate a starter diagram for you to modify...

1. Voter Authentication Service

Overview:

Handles voter authentication and eligibility verification. Ensures that each voter can vote only once per election and that only eligible voters can participate.

Responsibilities:

• Validate voter credentials using government-issued IDs or pre-registered accounts.
• Check voter eligibility for specific elections.
• Issue secure tokens for authenticated sessions.

2. Ballot Management Service

Overview:

Manages the creation, distribution, and configuration of ballots. Ensures that ballots are tailored to each election and securely distributed to eligible voters.

Responsibilities:

• Create ballots with candidate details and election-specific rules.
• Manage ballot start and end times.
• Provide secure and unique ballot access to eligible voters.

3. Vote Casting Service

Overview:

Processes votes securely while ensuring anonymity and integrity. Verifies the validity of submitted votes and prevents duplicate submissions.

Responsibilities:

• Accept encrypted votes from voters.
• Validate votes against election rules (e.g., one vote per voter).
• Store votes securely in an encrypted database.

4. Result Tabulation Service

Overview:

Aggregates votes and computes results. Provides real-time updates during voting and final results after the election ends.

Responsibilities:

• Count votes securely and accurately.
• Support multi-tier tabulation (e.g., district, state, national levels).
• Provide APIs for fetching live and finalized results.

5. Notification Service

Overview:

Sends notifications to voters about ballot availability, voting deadlines, and vote submission confirmations.

Responsibilities:

• Notify voters via email, SMS, or push notifications.
• Track delivery and status of notifications.
• Allow users to opt into election-specific notifications.

6. Audit and Logging Service

Overview:

Maintains immutable logs for all actions related to the voting process. Ensures auditability and transparency for post-election reviews.

Responsibilities:

• Record all activities (e.g., voter authentication, vote submission).
• Provide secure access to logs for election officials and auditors.
• Detect and flag suspicious activities.

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...

1. Voter Login and Authentication Request

Objective: Authenticate a voter and ensure eligibility for an election.

Steps:

1. API Gateway:
   • Receives the POST /api/auth/login request with voter credentials.
   • Validates the request and forwards it to the Voter Authentication Service.
2. Voter Authentication Service:
   • Validates credentials against the Voter Database.
   • Checks voter eligibility for the requested election.
   • Issues a session token for the voter.
3. Response:
   • Returns an authentication token and election eligibility status to the voter.

2. Retrieve Ballot Request

Objective: Fetch the ballot for an eligible election.

Steps:

1. API Gateway:
   • Receives the GET /api/ballots/{election_id} request with the voter’s session token.
   • Authenticates the voter and forwards the request to the Ballot Management Service.
2. Ballot Management Service:
   • Verifies the election ID and the voter’s eligibility.
   • Fetches the ballot data from the Ballot Database.
3. Response:
   • Returns the ballot (e.g., candidate names, rules) to the voter.

3. Cast Vote Request

Objective: Submit a vote securely for a specific election.

Steps:

1. API Gateway:
   • Receives the POST /api/votes/cast request with the encrypted vote.
   • Authenticates the voter and forwards the request to the Vote Casting Service.
2. Vote Casting Service:
   • Validates the vote (e.g., election ID, voter eligibility).
   • Ensures the voter hasn’t already voted for the election.
   • Stores the encrypted vote in the Votes Database.
3. Audit and Logging Service:
   • Logs the vote submission action for audit purposes.
4. Response:
   • Confirms successful vote submission to the voter.

4. Fetch Live Results Request

Objective: Retrieve live results during or after the election.

Steps:

1. API Gateway:
   • Receives the GET /api/results/live/{election_id} request.
   • Forwards the request to the Result Tabulation Service.
2. Result Tabulation Service:
   • Queries the Votes Database to aggregate votes for the election.
   • Computes live results based on the current vote count.
3. Response:
   • Returns live results (e.g., vote counts per candidate) to the client.

5. Notification Request

Objective: Notify voters about an upcoming election.

Steps:

1. Ballot Management Service:
   • Triggers a notification for voters in the election’s jurisdiction.
2. Notification Service:
   • Fetches voter contact details from the Voter Database.
   • Sends notifications via email, SMS, or push channels.
3. Response:
   • Confirms delivery status to the Ballot Management Service.

6. Audit Log Retrieval Request

Objective: Fetch logs for a specific election for auditing purposes.

Steps:

1. API Gateway:
   • Receives the GET /api/audit/logs/{election_id} request.
   • Authenticates the admin and forwards the request to the Audit and Logging Service.
2. Audit and Logging Service:
   • Queries the Audit Logs Database for the requested election ID.
   • Formats the logs for easy review.
3. Response:
   • Returns the audit logs to the admin.

Detailed component design

Dig deeper into 2-3 components and explain in detail how they work. For example, how well does each component scale? Any relevant algorithm or data structure you like to use for a component? Also you could draw a diagram using the diagramming tool to enhance your design...

1. Voter Authentication Service

End-to-End Working:

The Voter Authentication Service ensures only eligible voters can participate in an election. Upon receiving a login request, the service validates credentials against the voter database or external identity providers (e.g., government databases). Once authenticated, it checks voter eligibility for the election and issues a secure session token.

Communication:

• Protocols: REST APIs for communication with the API Gateway and external identity providers. gRPC for communication with the Ballot Management Service.
• Inter-Service Communication:
  • Receives requests from the API Gateway for voter authentication.
  • Sends eligibility confirmation to the Ballot Management Service.
  • Logs authentication actions with the Audit and Logging Service.

Data Structures/Algorithms:

• Hash Map for Credential Caching:
  • Caches hashed credentials for faster verification and reduced database load.
• Token-Based Authentication:
  • Uses JWT (JSON Web Token) for session management and secure inter-service communication.
• Access Control List (ACL):
  • Maps voter IDs to eligible elections to quickly determine voting rights.

Scaling for Peak Traffic:

• Horizontal Scaling:
  • Multiple stateless instances of the service handle concurrent authentication requests.
• Caching:
  • Implements Redis or Memcached to cache voter eligibility checks.
• Rate Limiting:
  • Prevents abuse by throttling excessive login attempts from the same user or IP.

Edge Cases:

• Duplicate Sessions:
  • Ensures existing sessions are invalidated when a new session is created.
• Identity Provider Downtime:
  • Falls back to cached eligibility data for a limited time during outages.

2. Ballot Management Service

End-to-End Working:

The Ballot Management Service creates, configures, and distributes ballots for elections. Election officials use this service to set up election rules, define candidates, and schedule voting times. It ensures only eligible voters can access ballots and manages ballot expiration.

Communication:

• Protocols: REST APIs for requests from the API Gateway. gRPC for secure communication with the Voter Authentication Service and Vote Casting Service.
• Inter-Service Communication:
  • Receives voter eligibility confirmation from the Voter Authentication Service.
  • Sends ballot data to the Vote Casting Service for vote validation.

Data Structures/Algorithms:

• JSON Schema Validation:
  • Validates ballot configurations to ensure compliance with election rules.
• Merkle Tree for Ballot Integrity:
  • Ensures tamper-evidence for ballots by hashing ballot data into a Merkle Tree.

Scaling for Peak Traffic:

• Database Sharding:
  • Distributes ballot data across multiple shards based on election IDs.
• Content Delivery Network (CDN):
  • Distributes static ballot content globally to reduce latency.

Edge Cases:

• Expired Ballots:
  • Ensures ballots are inaccessible after the election’s end time.
• Incorrect Ballots:
  • Allows administrators to update ballots while ensuring integrity.

3. Vote Casting Service

End-to-End Working:

The Vote Casting Service securely processes votes submitted by voters. It validates votes against election rules, ensures one vote per voter per election, and stores encrypted votes in the database. This service also generates a tamper-evident receipt for voters.

Communication:

• Protocols: REST APIs for receiving votes and gRPC for inter-service communication with the Ballot Management and Audit Services.
• Inter-Service Communication:
  • Retrieves ballot details from the Ballot Management Service.
  • Logs vote submissions with the Audit and Logging Service.

Data Structures/Algorithms:

• Homomorphic Encryption:
  • Encrypts votes to enable aggregation without decryption, preserving voter privacy.
• Bloom Filters:
  • Quickly checks if a voter has already cast a vote for the election.

Scaling for Peak Traffic:

• Asynchronous Processing:
  • Uses message queues (e.g., RabbitMQ) to handle vote validation and storage asynchronously.
• Horizontal Scaling:
  • Deploys multiple instances of the service to handle concurrent submissions.

Edge Cases:

• Duplicate Votes:
  • Implements idempotency using unique vote IDs to prevent double submissions.
• Tampered Votes:
  • Verifies integrity using cryptographic signatures.

4. Result Tabulation Service

End-to-End Working:

The Result Tabulation Service aggregates encrypted votes, decrypts results after the election ends, and generates real-time or final results. It supports tiered result breakdowns (e.g., district, state, national).

Communication:

• Protocols: REST APIs for result queries and gRPC for data exchange with the Vote Casting Service.
• Inter-Service Communication:
  • Fetches vote data from the Vote Casting Service.
  • Sends tabulated results to the API Gateway for client access.

Data Structures/Algorithms:

• MapReduce:
  • Aggregates votes across distributed shards for scalable result computation.
• End-to-End Encryption:
  • Decrypts aggregated votes only after verifying election completion.

Scaling for Peak Traffic:

• Parallel Processing:
  • Splits aggregation tasks across multiple compute nodes.
• Pre-Aggregation:
  • Computes intermediate results during the election to speed up final tabulation.

Edge Cases:

• Partial Results:
  • Flags incomplete results if some votes are delayed or corrupted.
• Result Discrepancies:
  • Provides detailed audit logs for result verification.

5. Audit and Logging Service

End-to-End Working:

The Audit and Logging Service records all critical actions in the voting process, such as voter authentication, vote submissions, and result tabulations. It ensures tamper-evident logs for post-election audits.

Communication:

• Protocols: REST APIs for retrieving logs and gRPC for receiving log entries from other services.
• Inter-Service Communication:
  • Receives log entries from all other services.
  • Sends verification data to election auditors.

Data Structures/Algorithms:

• Immutable Append-Only Logs:
  • Uses an append-only structure to ensure log integrity.
• Blockchain-Like Ledger:
  • Chains log entries with cryptographic hashes to prevent tampering.

Scaling for Peak Traffic:

• Partitioning:
  • Partitions logs by election ID for efficient storage and retrieval.
• Log Aggregators:
  • Uses tools like Fluentd or Logstash to collect and process logs at scale.

Edge Cases:

• Corrupted Logs:
  • Verifies integrity using cryptographic hashes before serving logs.
• Log Overload:
  • Implements log rotation and archiving to handle high volumes.

Trade offs/Tech choices

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

Homomorphic Encryption:

• Trade-off: Adds computational overhead but ensures vote privacy during aggregation.

Microservices Architecture:

• Trade-off: Increases operational complexity but enables independent scaling and fault isolation.

Blockchain-Like Audit Logs:

• Trade-off: High storage requirements but ensures tamper-proof integrity.

Failure scenarios/bottlenecks

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

Authentication Failures:

• Issue: High load on identity providers.
• Mitigation: Cache voter eligibility data.

Vote Submission Delays:

• Issue: Queue backlog during peak hours.
• Mitigation: Scale message queues dynamically.

Data Tampering:

• Issue: Unauthorized access to vote data.
• Mitigation: Use end-to-end encryption and multi-factor authentication.

Future improvements

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

Blockchain for Vote Storage:

• Decentralize vote storage for enhanced security and transparency.

AI-Powered Fraud Detection:

• Use machine learning to identify suspicious voting patterns in real-time.

Dynamic Scaling:

• Implement predictive scaling based on voting traffic trends.