Publish With Routing Keys

Routing keys allow messages to be routed selectively.

They are mainly used with:

• direct exchanges;
• topic exchanges.

---

Direct Routing

A direct exchange routes messages when the routing key matches exactly.

graph LR
    Publisher --> Exchange["orders"]
    Exchange -->|"orders.created"| Created["orders.created.queue"]
    Exchange -->|"orders.updated"| Updated["orders.updated.queue"]

var descriptor = new PublisherBoundDescriptor
{
    Exchanges =
    {
        new ExchangeBoundDescriptor
        {
            Name = "orders",
            Type = ExchangeTypes.Direct,
            Durable = true,
            Queues =
            {
                new QueueBoundDescriptor
                {
                    Name = "orders.created.queue",
                    Durable = true,
                    AutoDelete = false,
                    Binder = new BinderDescriptor
                    {
                        RoutingKey = "orders.created"
                    }
                },
                new QueueBoundDescriptor
                {
                    Name = "orders.updated.queue",
                    Durable = true,
                    AutoDelete = false,
                    Binder = new BinderDescriptor
                    {
                        RoutingKey = "orders.updated"
                    }
                }
            }
        }
    }
};

---

Topic Routing

A topic exchange routes messages using wildcard patterns.

graph TD
    Message["orders.eu.created"]
    Message --> EU["orders.eu.*"]
    Message --> AllOrders["orders.#"]

var descriptor = new PublisherBoundDescriptor
{
    Exchanges =
    {
        new ExchangeBoundDescriptor
        {
            Name = "orders",
            Type = ExchangeTypes.Topic,
            Durable = true,
            Queues =
            {
                new QueueBoundDescriptor
                {
                    Name = "orders.eu.queue",
                    Durable = true,
                    AutoDelete = false,
                    Binder = new BinderDescriptor
                    {
                        RoutingKey = "orders.eu.*"
                    }
                },
                new QueueBoundDescriptor
                {
                    Name = "orders.all.queue",
                    Durable = true,
                    AutoDelete = false,
                    Binder = new BinderDescriptor
                    {
                        RoutingKey = "orders.#"
                    }
                }
            }
        }
    }
};

---

Routing Key Naming

Prefer meaningful routing keys.

orders.created
orders.updated
payments.authorized
payments.completed

For topic exchanges, prefer hierarchical names.

orders.eu.created
orders.eu.updated
orders.us.created
orders.us.updated

---

Avoid

event1
event2
test
message

Routing keys should express business intent.