Let's design a new feature for the Facebook app: Ephemeral Groups. These groups function like regular Facebook groups but with a key difference: all content (posts, comments, media) within the group is automatically deleted after 24 hours. The group itself remains, but the content vanishes. Imagine users creating groups for flash events, temporary project collaborations, or just sharing memes that are only funny for a day.

Here are some considerations to guide our design:

1. Use Cases: What are the primary use cases for Ephemeral Groups? Consider examples beyond those mentioned above.
2. User Interface: How would users create and identify Ephemeral Groups within the existing Facebook app? How is it visually distinct?
3. Data Storage: How would you efficiently store and automatically delete content to minimize storage costs and ensure compliance with the 24-hour expiration?
4. Abuse Prevention: How do you prevent the misuse of Ephemeral Groups for sharing harmful or illegal content, given the disappearing nature of the data?
5. Notifications: How would notifications work for Ephemeral Groups? Should users receive notifications for content that will disappear soon?
6. Privacy: How would we make users aware of the ephemeral nature of the group and its content to manage their privacy expectations effectively?
7. Scalability: How would this feature scale to handle potentially millions of Ephemeral Groups without impacting the performance of the overall Facebook platform?

Walk me through your design proposal, addressing these considerations and any other relevant aspects you believe are important.

Ephemeral Groups Design Proposal

Let's design a new feature for Facebook called Ephemeral Groups. These groups will function like regular Facebook groups, but all content (posts, comments, media) within them is automatically deleted after 24 hours. The group itself remains, but the content vanishes.

1. Use Cases

• Flash Events: Organizing spontaneous gatherings, parties, or meetups.
• Temporary Project Collaboration: Quick brainstorming sessions or short-term project teams.
• Meme Sharing: Sharing content that's only relevant or funny for a short period.
• Study Groups: Sharing notes and discussing topics that are relevant for a specific test or assignment.
• Live Event Commentary: Real-time reactions and discussions during a live event (sports, concerts, etc.).
• Anonymous Feedback: Providing honest feedback on a topic without long-term records.

2. User Interface

• Group Creation:
  • Add a toggle during group creation: "Ephemeral Group" with a clear description of its behavior.
  • Upon enabling the toggle, a confirmation dialogue would explain the implications of ephemeral content. The confirmation needs to be very explicit and make it clear that content disappears after 24 hours, to avoid accidental creation of such a group.
• Visual Distinction:
  • Ephemeral Groups will have a distinct icon (e.g., a clock or a disappearing animation) next to the group name in the groups list and on the group page.
  • A banner at the top of the group page will remind users of the ephemeral nature of the content.
  • Posts within Ephemeral Groups could have a subtle visual cue (e.g., a slightly faded background or a timer icon) indicating their temporary status.
• Content Expiration Indicator: Display a countdown timer on each post showing the remaining time before it disappears. The countdown timer must be very visible.

3. Data Storage

• Separate Storage: Store Ephemeral Group content in a separate storage system or partition from regular Facebook content.
• Database: Use a NoSQL database (e.g., Cassandra, MongoDB) optimized for time-series data and efficient deletion.
  • Consider using TTL (Time-to-Live) features offered by these databases for automatic deletion.
• Object Storage: Store media content (images, videos) in object storage (e.g., AWS S3) with lifecycle policies for automatic deletion after 24 hours.
• Archiving (Optional): Implement a mechanism to archive content briefly (e.g., for a few hours) before final deletion for abuse investigation purposes (see Abuse Prevention section).
• Deletion Process:
  • A background process will periodically scan the Ephemeral Group storage and delete expired content.
  • The deletion process should be optimized to avoid performance bottlenecks.
  • Consider using batch deletion or asynchronous deletion queues.

4. Abuse Prevention

• Reporting Mechanism: Implement a reporting mechanism that allows users to flag inappropriate content within Ephemeral Groups.
• Content Moderation:
  • Even though content disappears, maintain a short-term archive (e.g., a few hours) for abuse investigations.
  • Utilize AI-powered content moderation tools to automatically detect and flag potentially harmful content in real-time.
  • Human moderators can review flagged content within the short-term archive and take appropriate action (e.g., ban users, delete groups).
• User Restrictions: Implement penalties for users who repeatedly violate community standards in Ephemeral Groups (e.g., temporary or permanent bans).
• Group Admin Controls: Provide group admins with tools to moderate content and manage members within their Ephemeral Groups.
• Keyword Filtering: Implement keyword filtering to prevent the sharing of certain prohibited terms or phrases.
• Watermarking: Consider watermarking media content to deter misuse and facilitate tracking if it's shared outside the platform before deletion.

5. Notifications

• Real-time Notifications: Send real-time notifications for new posts and comments within Ephemeral Groups, similar to regular groups.
• Expiring Content Notifications: Send notifications to users a few hours before their content is about to expire.
  • Allow users to opt-out of these notifications.
• Group Expiration Reminders: Periodically remind users of the ephemeral nature of the group and its content.
• Do Not Over-Notify: Limit the frequency of notifications to avoid overwhelming users.

6. Privacy

• Clear Disclosure: Prominently display warnings and disclaimers about the ephemeral nature of the group and its content during group creation and within the group itself.
• Privacy Settings: Allow users to control who can see their posts and comments within Ephemeral Groups (e.g., only group members, friends of members).
• Data Retention Policy: Clearly state the data retention policy for Ephemeral Groups in the Facebook Privacy Policy.
• Avoid Assumptions: Do not assume users understand the ephemeral nature of the group. Remind them frequently and explicitly.

7. Scalability

• Distributed Architecture: Use a distributed architecture to handle a large number of Ephemeral Groups and their content.
• Caching: Implement caching mechanisms to reduce the load on the database and object storage.
• Asynchronous Processing: Use asynchronous processing for tasks like content deletion and notification delivery.
• Load Balancing: Use load balancing to distribute traffic across multiple servers.
• Database Sharding: Shard the database to distribute the data across multiple servers.
• Auto-Scaling: Implement auto-scaling to automatically adjust resources based on demand.
• Content Delivery Network (CDN): Use a CDN to cache and deliver media content to users quickly and efficiently.
• Optimize Queries: Optimize database queries to improve performance.

Tradeoffs

Feature	Pros	Cons
Ephemeral Nature	Encourages candid and spontaneous content, reduces long-term storage	Potential for misuse, loss of valuable information, harder moderation
TTL in Database	Automatic deletion, simplifies data management	Requires careful configuration, potential for data loss if misconfigured
Separate Storage	Isolates Ephemeral Group data, optimizes deletion	Increased infrastructure complexity, higher storage costs
Short-Term Archive	Facilitates abuse investigation	Increases storage requirements, adds complexity to deletion process

Other Approaches

• Option 1: Implement Ephemeral Groups as a type of regular group.
  • Pros: Simpler implementation, leverages existing group infrastructure.
  • Cons: May impact performance of regular groups, requires careful management of deletion process.
• Option 2: Integrate Ephemeral functionality into existing features like Stories.
  • Pros: Leverages existing user behavior, avoids creating a new feature from scratch.
  • Cons: May not be suitable for all use cases, limits the scope of Ephemeral Groups.

Edge Cases

• User uploads content right before the 24-hour deletion. Ensure the deletion process handles this scenario correctly.
• User edits content shortly before deletion. Update the deletion timer accordingly.
• A group admin changes the group type from regular to ephemeral (or vice-versa). Handle the transition of existing content appropriately.
• Facebook experiences a system outage. Ensure the deletion process resumes correctly after the outage.
• Users in different time zones. Make sure content expiration is consistent regardless of the user's time zone.

Future Considerations

• Customizable Expiration Times: Allow group admins to set custom expiration times for content (e.g., 1 hour, 6 hours, 12 hours).
• Content Archiving (User Choice): Allow users to optionally archive their content before it expires.
• Integration with other Facebook features: Integrate Ephemeral Groups with other Facebook features like Events, Marketplace, and Dating.
• Advanced Moderation Tools: Provide group admins with more advanced moderation tools, such as the ability to automatically flag content based on keywords or user behavior.
• Expand Use Cases: Explore new use cases for Ephemeral Groups based on user feedback and data analysis.