Why do we need a Bill of Materials?
Ok, that sounds cool, but why do we really need a BOM in Mule? These are the most common problems and real-life scenarios where dependencies management becomes a challenge:Version Conflict resolution
- In our mule apps, especially when we are using transitive dependencies, we might find that we’ve got two or more of our dependencies pointing to another dependency, but with different versions.
- Without a BOM, developers might have to manually override dependency versions to ensure compatibility between libraries, which can be tedious and error-prone.
- A BOM defines a set of compatible versions for multiple dependencies, ensuring that all components work together properly. This eliminates the need for manually resolving conflicts.
Consistency Across Connectors in all of our Mule Apps:
- In our Mulesoft Application Network, we may find different applications using the same connectors (or other dependencies). It’s very important that all apps using the same connector have the same version.
- The BOM allows us to manage these versions in one place. When the BOM is imported, all modules inherit the same versions of the dependencies, maintaining version consistency.
Simplified Dependency Management:
- When using multiple dependencies from MuleSoft, each dependency might have its own set of transitive dependencies. Managing these dependencies and ensuring compatibility between their versions can be complicated.
- A BOM simplifies this by specifying all the versions in a single location. We can import the BOM into our mule project, and Maven will use the predefined versions of those dependencies without needing to specify versions for each dependency explicitly.
Easier Upgrades and Maintenance:
- When it’s time to upgrade, especially connectors, we can simply update the BOM’s version instead of updating the version numbers of all of our apps using a connector. This ensures that you’re using a set of dependencies that are known to work together, and upgrading becomes much simpler and controlled.
What is a BOM?
The BOM file is essentially a POM with dependency management, and it often only specifies versions of dependencies, without adding actual project-specific functionality.In other words, a BOM is a special type of
pom.xml that defines a set of dependency versions. When a project imports a BOM, it inherits the versions of dependencies specified in the BOM without needing to define them individually in its own pom.xml. This ensures that all projects using the BOM are aligned on the same dependency versions, promoting consistency and compatibility.This approach simplifies dependency management, reduces version conflicts, and streamlines the build process, especially in large-scale with multiple Mule apps and APIs.
What goes into a BOM?
As mentioned above, a BOM is a special type of POM file. Here’s why: the BOM file will list dependencies and their versions without packaging anything. For example, we could list 10 or 100 connector dependencies with their versions, but when compiling the project Maven will not include those dependencies in the final jar.Dependencies
To list dependencies in a BOM file, there’s a specific section in the file called dependencyManagement.The BOM file uses the
<dependencyManagement> section to declare versions of dependencies. However, unlike regular dependencies in the dependencies section of our pom files, the dependencies listed in <dependencyManagement> are not automatically included in your project unless explicitly declared.For example, a BOM file for our Mule apps might define a set of connector dependencies like this:
<project>
...
<dependencyManagement>
...
<dependencies>
<dependency>
<groupId>org.mule.connectors</groupId>
<artifactId>mule-http-connector</artifactId>
<version>${http.connector.version}</version>
<classifier>mule-plugin</classifier>
</dependency>
<dependency>
<groupId>org.mule.connectors</groupId>
<artifactId>mule-sockets-connector</artifactId>
<version>${sockets.connector.version}</version>
<classifier>mule-plugin</classifier>
</dependency>
...
</dependencies>
</dependencyManagment>
...
</project>
Plugins
Similarly, we can use the BOM file to list plugins and their versions. For plugins, we’ll use the section pluginManagement. This section, however, will go within the build section of the bom file (same as we do with normal pom files). The behaviour will be the same as with the dependencyManagement section. All the plugins within the pluginManagement element will not be included by Maven in the final jar package.For example, a BOM file for our Mule apps could define the following list of plugins:
<project>
...
<build>
<pluginManagement>
<plugins>
...
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-resources-plugin</artifactId>
<version>${maven.resources.version}</version>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-clean-plugin</artifactId>
<version>${maven.clean.version}</version>
</plugin>
<plugin>
<groupId>org.mule.tools.maven</groupId>
<artifactId>mule-maven-plugin</artifactId>
<version>${mule.maven.plugin.version}</version>
<extensions>true</extensions>
<configuration>
<classifier>mule-plugin</classifier>
</configuration>
</plugin>
...
</plugins>
</pluginManagement>
</build>
...
</project>
As you can see, this makes the BOM an essential tool for an organization with multiple Mule apps, where multiple dependencies need to work together in a consistent and predictable manner.
In the next post, we’ll get our hands on it and see How to Define a BOM for our Mule Apps.
In the next post, we’ll get our hands on it and see How to Define a BOM for our Mule Apps.