Amazon DocumentDB

  • Fully managed document database service designed to be fast, scalable, and highly available.
  • Data is stored in JSON-like documents.
  • Compatible with MongoDb.
  • Flexible schema and indexing.
  • Commonly used for content management, user profiles, and real-time big data.

How it Works

how does amazon documentdb work

  • An Amazon DocumentDB cluster decouples storage and compute.
  • A cluster consists of Cluster volume and Instances
    • Cluster volume refers to the storage layer that spans multiple Availability Zones. Each Availability Zone has a copy of the cluster data.
    • Instances refers to the compute layer. It provides the processing power needed for the database to write data to, and read data from, the cluster volume. 
  • Amazon DocumentDB Endpoints
    • Cluster endpoint
      • Connects to cluster’s current primary instance.
      • Can be used for both read and write operations.
    • Reader endpoint
      • Connects to one of the available replicas of the cluster.
      • Use for read operations only.
      • If the cluster has more than one replica, the reader endpoint will direct each request to DocumentDB replicas.
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    • Instance endpoint
      • Connects to a specific instance in the cluster.
      • Use for specialized workloads that will only affect specific replica instances.

Performance

  • Provides millions of requests per second with millisecond latency and has twice the throughput of MongoDb.

Scaling

  • The minimum storage is 10GB. The Amazon DocumentDB storage will automatically scale up to 64 TB in 10 GB increments without affecting performance.
  • The Amazon DocumentDB cluster can be scaled by modifying the instance class for each instance in the cluster.
  • You can create up to 15 Amazon DocumentDB replicas in the cluster.
  • The replication lag is usually less than 100 milliseconds after the primary instance has written an update.

Reliability

  • The cluster volume provides durability by maintaining six copies of all data across three Availability Zones.
  • Amazon DocumentDB uses asynchronous replication to update the changes made to the primary instance to all of DocumentDB’s read replicas.
  • In most cases, the DocumentDB’s restart time is less than a minute after a database crash.
  • DocumentDB replicas can act as a failover target with no data loss.
  • Supports automatic failover.
  • Supports promotion priority within a cluster. Amazon DocumentDB will promote the replica with the highest priority tier to primary when the primary instance fails.
  • To increase the cluster’s availability, create replicas in multiple Availability Zones. The Amazon DocumentDB will automatically include the replicas when selecting for a failover target in the event of an instance failure.

Backup And Restore

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  • Automated backups are always enabled.
  • Supports Point-In-Time restoration, which can be up to 5 minutes in the past.
  • You can restore from a cluster snapshot.
  • Supports sharing of encrypted manual snapshots.

Security

  • You can authenticate a connection to a DocumentDB database through standard MongoDb tools with Salted Challenge Response Authentication Mechanism (SCRAM).
  • You can authenticate and authorize the use of DocumentDB management APIs through the use of IAM users, roles, and policies.
  • Data in transit is encrypted using Transport Layer Security (TLS).
  • Data at rest is encrypted using keys you manage through AWS KMS.
  • Amazon DocumentDB supports role based access control ( RBAC ) with built-in roles to enforce the principle of least privileged access.

Pricing

  • You are billed based on four categories
    • On-demand instances
      • Pricing per second with a 10-minute minimum
    • Database I/O
      • Pricing per million I/Os
    • Database Storage
      • Pricing per GB/month
    • Backup Storage
      • Pricing per GB/month

Limitations

  • Amazon DocumentDB does not support cross-region replicas.
  • Encryption of an existing DocumentDB instance is not supported.
  • Sharing of automatic DB snapshots to other accounts is not allowed. A workaround for this is to manually copy the snapshot from the automatic snapshot, then, copy the manual snapshot to another account.

Note: If you are studying for the AWS Certified Database Specialty exam, we highly recommend that you take our AWS Certified Database – Specialty Practice Exams and read our Database Specialty exam study guide.

AWS Certified Database Specialty Practice Exams

Sources:
https://aws.amazon.com/documentdb/faqs/
https://aws.amazon.com/blogs/database/migrating-to-amazon-documentdb-with-the-online-method/

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