Alibaba Cloud Simple Message Queue (SMQ, formerly MNS) is a distributed messaging service that provides scalability, high efficiency, reliability, security, and availability. SMQ allows developers to transfer data and notifications between the distributed components of an application and build a loosely coupled system. SMQ provides a queue-based messaging model and a topic-based messaging model.
Access methods
SMQ supports access from the Internet and Virtual Private Cloud (VPC). If you select VPC as the network type, you can configure the CIDR block, route table, and gateway of your VPC. In your VPC, you can use Alibaba Cloud resources, such as Elastic Compute Service (ECS), ApsaraDB RDS, and Server Load Balancer (SLB) instances.
Queue-based messaging model
A queue-based messaging model provides highly reliable and concurrent message consumption services. Each message in a queue can be consumed by only one client.
An SMQ queue can be compared to a conveyor belt sushi restaurant. Chefs (producers) produce sushi dishes (messages) and put them on the conveyor belt. Each sushi dish is unique. Customers (consumers) can take (consume) their favorite sushi dishes from the conveyor belt.
Queue-based message flow
The below figure Queue-based message flow illustrates the process of queue-based messaging. In this flow, producers send messages to a queue, while consumers retrieve the messages from the queue.
Figure 1. Queue-based message flow
Features of the queue-based messaging model
Multiple queue modes
Standard queues and delayed queues are supported. You can customize the parameters of a queue to meet various business needs.
Concurrent access requests
SMQ queues can process a large number of concurrent requests from multiple producers and consumers. Once a message is pulled from a queue, it cannot be retrieved again within a specified period.
Guaranteed message delivery
SMQ ensures that a message in a queue can be consumed at least once during the validity period of the message. SMQ is integrated into the Alibaba Cloud account system in which resources are isolated between users. This ensures that only authorized entities can retrieve your messages in SMQ queues.
Log management
You can view the log of each message. The log includes all records that are generated when you send, receive, and delete the message during its lifecycle. For more information, see Log management.
Cloud Monitor
You can view queue information and customize alert rules in the Cloud Monitor console. Then, Cloud Monitor sends notifications to you if an unexpected issue occurs. For more information, see Cloud Monitor.
Topic-based massaging model
A topic-based messaging model is used to send messages from one publisher client to multiple subscriber clients. SMQ topics can be pushed as messages by using multiple methods.
A topic can be compared to a newspaper to which multiple customers subscribe. When a new issue of the newspaper is released, customers (including the partners of the post office) can select one of the following methods to receive the newspaper:
Ask a mail courier to deliver the newspaper to a specific address, such as your house.
Go to the nearest newsstand to which a mail courier delivers the newspaper.
Topic-based message flow
As shown in a topic-based message flow:
A topic has multiple subscriptions that are specified with different queues.
After a message is published to the topic, the message is pushed to the queue endpoints that are specified in subscriptions.
Subscriptions support message filtering. You can specify a tag for a subscription to filter messages.
If you do not specify a tag for a subscription, messages are pushed to the specified queue no matter whether you specify message tags.
If you specify a tag for a subscription, only the messages that have the tag can be pushed to the specified queue.
Figure 2. Topic-based message flow
Features of the topic-based messaging model
Notification messages
The SMQ server pushes messages to specified queues. This eliminates unnecessary request polling and resource consumption of clients. You can maximize the resource usage to meet your business needs. You do not need to depend on other message service clients. This prevents system instability that is caused by excess code introduction. For more information, see Sign a request that is sent to an endpoint and Manage topics.
If a callback URL is not available due to network or other reasons, you can push messages to SMQ queues and retrieve messages from the queues. You can use queues to consume messages from topics. For more information, see Queue and Send messages from one producer client to multiple consumer clients.
One-to-many
A message that is published to a topic can be pushed to multiple subscriber clients.SMQ pushes messages to queues that are specified in subscriptions. After a message is published, the message is pushed to multiple endpoints. This ensures the atomicity of message publishing.
Tag-based message filtering
SMQ allows you to use tags to filter messages. You can specify a tag for a subscription and then receive only the messages that have the tag from the topic. SMQ pushes the message to the endpoint that is specified only when the tags are the same. For more information, see RESTful API operations about topics.
Message delivery
SMQ sends messages to queues. For more information, see Queue and Send messages from one producer client to multiple consumer clients.
Guaranteed message delivery: The messages that are published to a topic are automatically pushed to subscriber clients during the validity period based on specified retry policies and content formats. For more information, see NotifyStrategy.
Message formats
XML: The message is in XML format and contains the message body and message attributes.
JSON: The message is in JSON format and contains the message body and message attributes.
SIMPLIFIED: The message body is a message that is published by a user. It does not contain attribute information (this a simplified format, namely, text format). For more information, see:
Log management
Logs are generated when a message is published to a topic and then pushed to endpoints. The information about push retries and results are recorded in logs. You can use logs to view the lifecycle of the message. Log management allows you to troubleshoot issues with ease. For more information, see Log management.
Cloud Monitor
Cloud Monitor records messages that are pushed. If one or more messages fail to be pushed, Cloud Monitor allows you trace exceptions by creating alert rules. For more information, see Cloud Monitor.