ActiveMQ vs Amazon SQS: What are the differences?

ActiveMQ is an open-source message broker that supports multiple messaging protocols, while Amazon SQS (Simple Queue Service) is a fully managed message queuing service provided by AWS. Let's explore the key differences between them.

1. Message Delivery Model: ActiveMQ follows a traditional message queue model, where the messages are stored in queues and clients consume them in a sequential order. On the other hand, Amazon SQS follows a distributed messaging model, where messages are automatically distributed among multiple queues and processing is parallelized. This provides better scalability and fault tolerance.

2. Message Ordering: ActiveMQ guarantees the ordered delivery of messages within a single queue, ensuring that messages are consumed in the same order as they are produced. In contrast, Amazon SQS does not guarantee strict ordering of messages, as it distributes messages across different servers and processing can happen in parallel. However, you can use message groups in Amazon SQS to ensure ordering of messages within a specific group.

3. Message Persistence: ActiveMQ stores messages in a persistent manner, ensuring that they are not lost even in the case of server failures. It provides options for different persistence stores, such as relational databases or file systems. On the other hand, Amazon SQS stores messages redundantly across multiple availability zones, providing durability and high availability. It does not provide direct control over the persistence of individual messages.

4. Message Visibility: ActiveMQ allows consumers to acknowledge the receipt of messages, making them invisible to other consumers. This ensures exclusive processing of messages by a single consumer. In Amazon SQS, messages become invisible as soon as they are received by a consumer. However, if the consumer fails to process the message within a specified visibility timeout period, the message becomes visible again and can be consumed by another consumer.

5. Message Size Limit: ActiveMQ has a limit on the maximum size of messages that can be processed. The limit is typically based on the underlying persistence store. Amazon SQS supports larger message sizes compared to ActiveMQ. The maximum message size in Amazon SQS is 256KB for standard queues and 2GB for FIFO queues.

6. Message Delay: ActiveMQ does not provide a built-in delay mechanism for delivering messages. However, it can be achieved using custom code or frameworks built on top of ActiveMQ. In Amazon SQS, you can set a delay on individual messages, specifying the time to wait before making the message visible to consumers. This can be useful in scenarios where messages need to be processed after a specific delay.

In summary, ActiveMQ follows a traditional message queue model with strict ordering and more control over persistence and message visibility. Amazon SQS, on the other hand, follows a distributed messaging model with automatic distribution and parallel processing, providing scalability and high availability. It has features such as message groups, larger message size support, and a built-in delay mechanism.