MongoDB Atlas vs Amazon DocumentDB: A Comprehensive Pricing Comparison

When choosing between MongoDB Atlas and Amazon DocumentDB, pricing plays a crucial role in the decision-making process. Let’s analyze their pricing models across different application scales.

Baseline Evaluation Criteria

Before diving into the comparison, let’s establish our evaluation criteria:

1. Instance Types: Computing power and memory specifications
2. Storage Costs: Price per GB of data stored
3. I/O Operations: Cost of read/write operations
4. Data Transfer: Network transfer costs
5. Backup Storage: Costs for maintaining backups
6. Minimum Commitment: Required minimum infrastructure

Small-Scale Applications (0-50GB data)

MongoDB Atlas

• Starting Price: Free tier available (512MB - 5GB)
• Shared Clusters: From $0.08/hour ($57/month)
• Storage: Included in instance price up to quota
• Backup: Included for shared clusters
• Best For: Development, testing, small production workloads

Amazon DocumentDB

• Starting Price: No free tier
• Minimum Instance: db.t3.medium at $0.078/hour ($57/month)
• Storage: $0.10 per GB-month
• Backup: No additional charge for up to 100% of storage
• Best For: Small production workloads within AWS ecosystem

Medium-Scale Applications (50-500GB data)

MongoDB Atlas

• M40 Cluster: ~$0.68/hour ($491/month)
• Storage: Included up to 128GB, then $0.08 per GB-month
• IOPS: Included in instance price
• Backup: Included for first 8GB, then $0.025/GB-month

Amazon DocumentDB

• db.r5.xlarge: $0.60/hour ($438/month)
• Storage: $0.10 per GB-month
• I/O: $0.20 per million requests
• Backup: No additional charge for up to 100% of storage

Large-Scale Applications (500GB+ data)

MongoDB Atlas

• M80 Cluster: ~$1.39/hour ($1,010/month)
• Storage: $0.08 per GB-month after included storage
• Multi-region: Additional costs for cross-region replication
• Enterprise Support: Starting at $5,000/month

Amazon DocumentDB

• db.r5.2xlarge: $1.20/hour ($876/month)
• Storage: $0.10 per GB-month
• I/O: $0.20 per million requests
• Multi-AZ: 2x instance cost for high availability
• AWS Enterprise Support: Based on AWS bill percentage

Cost-Saving Considerations

MongoDB Atlas

• Automatic scaling
• Pay-per-hour billing
• Free tier for development
• Built-in monitoring tools
• No separate backup infrastructure needed

Amazon DocumentDB

• Reserved instances (up to 69% savings)
• Integration with AWS services
• Consolidated AWS billing
• Auto-scaling storage
• Cross-region backup copies included

Real-World Cost Examples

Example 1: Basic Production App

• 50GB data
• 100,000 operations/day
• Single region

MongoDB Atlas: ~$200/month DocumentDB: ~$235/month

Example 2: Enterprise Application

• 1TB data
• 1M operations/day
• Multi-region deployment

MongoDB Atlas: ~$2,500/month DocumentDB: ~$2,800/month

Recommendation Framework

1. Choose MongoDB Atlas if:

   • You need a free tier for development
   • Multi-cloud deployment is required
   • Prefer fully-managed service with less operational overhead

2. Choose Amazon DocumentDB if:

   • Already heavily invested in AWS ecosystem
   • Need tight integration with AWS services
   • Can benefit from reserved instance pricing
   • Have existing AWS Enterprise Support

Conclusion

MongoDB Atlas generally offers more flexible pricing for smaller workloads due to its free tier and shared clusters. DocumentDB becomes more cost-competitive at larger scales, especially when using reserved instances and existing AWS infrastructure. The final choice often depends on your existing cloud infrastructure, technical requirements, and long-term scaling plans.

Remember to factor in the hidden costs like data transfer, operational overhead, and support when making your decision. Also, consider running a proof-of-concept with your specific workload to get accurate pricing estimates.