feat(blog): add release notes for 2.4 release (#634)

Co-authored-by: Alejandra Quetzalli  <[email protected]>

pages/blog/release-notes-2.4.0.md

@@ -0,0 +1,137 @@
+---
+title: AsyncAPI Spec 2.4.0 Release Notes
+date: 2022-04-28T09:00:00+01:00
+type: Communication
+tags:
+  - Specification
+  - Release Notes
+cover: /img/posts/release-notes-2.4.0/cover.webp
+authors:
+  - name: Sergio Moya
+    photo: /img/avatars/smoya.webp
+    link: https://twitter.com/smoyac
+    byline: Pilot at AsyncAPI Airlines
+excerpt: 'AsyncAPI 2.4 is now released. This brings really helpful additions, such as the new `messageId` field, Server Variables reusability, and security at Operation level'
+featured: true
+---
+
+The new version of the AsyncAPI specification - 2.4.0 - is now available.
+
+> This is a minor release, and it doesn't bring any breaking changes. You can switch to it by modifying the following value in your AsyncAPI file `asyncapi: '2.3.0'` into `asyncapi: '2.4.0'`
+
+## Message uniqueness thanks to the new messageId field
+
+As operations have `OperationId`, AsyncAPI messages can now define `messageId`. This new field is used to identify a message across a whole AsyncAPI document uniquely.
+This new field will be helpful in tools that ask the user to select a message as input, such as validating their schema or filtering code to be generated.
+
+For example:
+
+```yaml
+asyncapi: 2.4.0
+components:
+  messages:
+    SomeMessage:
+      messageId: SomeMessage
+      payload:
+        type: object
+        properties:
+          name:
+            type: string
+```
+
+This new feature was contributed by [Waleed Ashraf](https://github.com/WaleedAshraf).
+For more detail, see [Waleed's `/spec #751`pull request](https://github.com/asyncapi/spec/pull/751) and the [Github issue where Waleed's `MessageId` feature addition was discussed](https://github.com/asyncapi/spec/issues/458).
+
+## Server Variables can be now referenced from components
+
+To allow for more flexibility in how AsyncAPI documents are structured and enable content to be reused, `serverVariables` can now be defined as reusable components.
+
+For example:
+
+```yaml
+asyncapi: 2.4.0
+servers:
+  development:
+    $ref: '#/components/servers/myserver'
+  production:
+    $ref: '#/components/servers/myserver'
+components:
+  servers:
+    myserver:
+      url: "{stage}.my-server.com:{port}"
+      protocol: ws
+      variables:
+        stage:
+          $ref: "#/components/serverVariables/stage"
+        port:
+          $ref: "#/components/serverVariables/port"
+  serverVariables:
+    stage:
+      default: dev
+    port:
+      enum: [5000, 6000]
+      default: 5000
+```
+
+These are added to the many other aspects of the AsyncAPI specification which can be declared as reusable components. You can see the full list in the [Components Object section of the AsyncAPI specification](https://www.asyncapi.com/docs/specifications/v2.4.0#componentsObject).
+
+This new feature was contributed by [Daniel Kocot](https://github.com/danielkocot). For more detail, see [Daniel's `/spec #717` pull request](https://github.com/asyncapi/spec/pull/717) and the [Github issue where Daniel's change to `serverVariables ` was discussed](https://github.com/asyncapi/spec/issues/707).
+
+## Security can now be defined at Operation level
+
+Until today, Security requirements were defined at Server level. That restricted the security requirements to be the same for all channels linked with a Server, and for all operations of those channels.
+In fact, when setting Security in both the Server and the Operation, both should be satisfied.
+
+For example:
+
+```yaml
+asyncapi: 2.4.0
+servers:
+  production:
+    url: "mykafkacluster.org:8092"
+    protocol: kafka-secure
+    security:
+      - service_auth:
+         - auth:write
+         - auth:read
+channels:
+  some/events:
+    servers:
+      - production
+    subscribe:
+      # This operation level security implies the ability to subscribe to messages from
+      # `some/events` channel with Authorization headers 
+      # that have `auth:read` scope. Note that an operation level security must still satisfy 
+      # security requirements specified at the server level.
+      security:
+        - service_auth:
+          - auth:read  
+```
+
+Thanks to [Sekharbans](https://github.com/sekharbans-ebay), is now possible to increase security granularity by defining a set of security requirements at Operation level. For more detail, see [Sekharban's `/spec #584` pull request](https://github.com/asyncapi/spec/pull/584) and the [Github issue where Sekharban's suggested feature was discussed](https://github.com/asyncapi/spec/issues/584).
+
+## Reusability of Servers defined in Components is clarified in the specification
+
+Reusability of Servers was introduced in [AsyncAPI 2.3.0](https://www.asyncapi.com/blog/release-notes-2.3.0#servers-and-channels-can-now-be-defined-as-reusable-components). However, the change was not fully clarified in the specification, leading to confusion.
+
+Thanks to [Vladimir Gorej](https://github.com/char0n), this is now clarified by mentioning that elements for the Servers Object can be either Server Object or a Reference Object.
+For more detail, see [Vladimir's `/spec #706`pull request](https://github.com/asyncapi/spec/pull/706) and the [Github issue where Vladimir's Servers Object change was discussed](https://github.com/asyncapi/spec/issues/705).
+
+## Tooling support
+
+The following official AsyncAPI tools are already updated to support 2.4.0 version of the specification:
+- JSON Schema that supports validation of AsyncAPI documents is updated in [this](https://github.com/asyncapi/spec-json-schemas) repository. Also **@asyncapi/specs** package has been updated on NPM to version `2.14.0`, and it contains the 2.4.0 JSON Schema.
+- [JavaScript Parser](https://github.com/asyncapi/parser-js/) uses latest **@asyncapi/specs** package and can be used to parse and validate 2.4.0 documents. Upgrade to `1.15.0` version.
+- [HTML template](https://github.com/asyncapi/html-template) uses the latest **@asyncapi/react-component** package. Upgrade to `0.24.9` version.
+- [JavaScript Converter](https://github.com/asyncapi/converter-js/) enables conversion from any AsyncAPI version into the 2.4.0 version of the spec. Upgrade to `0.11.0` version.
+- [Generator](https://github.com/asyncapi/generator/) uses the latest @asyncapi/parser package, so while generating output, it can validate 2.4.0 documents. Upgrade to `1.9.3` version.
+
+Last but not least is the AsyncAPI Studio. [Check out the Studio with this example](https://studio.asyncapi.com/?url=https://raw.githubusercontent.com/asyncapi/spec/v2.4.0/examples/websocket-gemini.yml).
+
+## Look ahead
+
+We aim to have a regular cadence of releases of the AsyncAPI specification, four times a year. For more information about when to expect future releases, you can see our [release process document](https://github.com/asyncapi/spec/blob/master/RELEASE_PROCESS.md#release-cadence).
+
+We're also working on the next major release of the AsyncAPI specification: 3.0.0. If you'd like to contribute, or just follow the discussions, you can see [Work on 3.0 release issue](https://github.com/asyncapi/spec/issues/691).
+
+> Photo by <a href="https://unsplash.com/@andurache?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Alexandru Tudorache</a> on <a href="https://unsplash.com/?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText">Unsplash</a>