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Deploying User Codes on the Member

Hazelcast can dynamically load your custom classes or domain classes from other members. A lite member can be designated as a class repository, but any member can provide classes to other members. For this purpose Hazelcast offers a distributed dynamic class loader.

The following is a brief working mechanism of the User Code Deployment feature:

  1. A new dynamic class loader is created to handle each operation.

  2. It first checks locally available classes, i.e. the member’s classpath. If the class is found, it is used.

  3. Then it checks the cache of classes loaded from remote members or clients (if caching is enabled on your local member, see the Configuring User Code Deployment section). If your class is found there, it is used.

  4. Finally, the dynamic class loader checks configured remote members, one by one. If some member returns the class, it will be used. It can also put this class into the local class cache as mentioned in the previous step.

  5. If the class is not found, ClassNotFoundException is thrown.

  6. The dynamic class loader is released after the operation is handled. A next operation will load the class from the cache or re-fetch it.

Configuring User Code Deployment

User Code Deployment feature is not enabled by default. You can control local caching of the classes loaded from other members, control classes to be provided to other members and create blacklists and whitelists of classes and packages.

Following are example configuration snippets:

Declarative Configuration:

<hazelcast>
    ...
    <user-code-deployment enabled="true">
        <class-cache-mode>ETERNAL</class-cache-mode>
        <provider-mode>LOCAL_CLASSES_ONLY</provider-mode>
        <blacklist-prefixes>com.foo</blacklist-prefixes>
        <whitelist-prefixes>com.bar.MyClass</whitelist-prefixes>
        <provider-filter>HAS_ATTRIBUTE:lite</provider-filter>
    </user-code-deployment>
    ...
</hazelcast>

Programmatic Configuration:

        Config config = new Config();
        UserCodeDeploymentConfig distCLConfig = config.getUserCodeDeploymentConfig();
        distCLConfig.setEnabled( true )
                .setClassCacheMode( UserCodeDeploymentConfig.ClassCacheMode.ETERNAL )
                .setProviderMode( UserCodeDeploymentConfig.ProviderMode.LOCAL_CLASSES_ONLY )
                .setBlacklistedPrefixes( "com.foo" )
                .setWhitelistedPrefixes( "com.bar.MyClass" )
                .setProviderFilter( "HAS_ATTRIBUTE:lite" );

User Code Deployment on the member has the following configuration:

  • enabled: Specifies whether dynamic class loading is enabled or not. Its default value is "false" and it’s a mandatory attribute. If feature is disabled, the member will never load classes from other members or clients.

  • <class-cache-mode>: Controls the local caching behavior for the classes loaded from remote members (classes loaded from clients are always cached). Available values are:

    • ETERNAL: Cache the loaded classes locally. This is the default value and suitable when you load long-living objects, such as domain objects stored in a map.

    • OFF: Do not cache the loaded classes locally. It is suitable for loading runnables, callables, entry processors, etc.

  • <provider-mode>: Controls which classes are served to other cluster members. Available values are:

    • LOCAL_AND_CACHED_CLASSES: Serve classes loaded from both local classpath and from other members. This is the default value.

    • LOCAL_CLASSES_ONLY: Serve classes from the local classpath only. Classes loaded from other members are used locally, but they are not served to other members.

    • OFF: Never serve classes to other members.

  • <blacklist-prefixes>: Comma separated class/package name prefixes that the member will never attempt to load from other members and that the client won’t be allowed to upload. For example, if you set it to "com.foo", remote loading of all classes from the "com.foo" package is prevented, including the classes from all its sub-packages. If you set it to "com.foo.Class", then "Class" and all classes starting with "Class" in the "com.foo" package are blacklisted. There are built-in prefixes which are always blacklisted. These are as follows:

    • javax.

    • java.

    • sun.

    • com.hazelcast.

  • <whitelist-prefixes>: Comma separated name prefixes of classes/packages only from which the classes are allowed to be loaded. It allows to quickly configure remote loading only for classes from selected packages. It can be used together with blacklisting. For example, you can whitelist the prefix "com.foo" and blacklist the prefix "com.foo.secret". If the list is empty, all classes are allowed.

  • <provider-filter>: Filter to constrain members that can be used for a class loading request when a class is not available locally. The value is in the format "HAS_ATTRIBUTE:foo". When it is set to "HAS_ATTRIBUTE:foo", the class loading request is only sent to the members which have "foo" as a member attribute. Setting this to null allows loading of classes from all members. See an example in the next section.

Example for Filtering of Members

As described above, the configuration element provider-filter is used to limit members that can be used to load classes. The attribute required in the provider-filter must be set as a member attribute on the members from which the classes are to be loaded. See the following examples provided as programmatic configurations.

The below example configuration allows the Hazelcast member to load classes only from the members with the class-provider attribute set. It does not ask any other member to provide a locally unavailable class:

Config hazelcastConfig = new Config();
DistributedClassloadingConfig distributedClassloadingConfig = hazelcastConfig.getDistributedClassloadingConfig();
distributedClassloadingConfig.setProviderFilter("HAS_ATTRIBUTE:class-provider");

HazelcastInstance instance = Hazelcast.newHazelcastInstance(hazelcastConfig);

And the below example configuration sets the attribute class-provider for a member. So, the above member loads classes from the members who have the attribute class-provider:

Config hazelcastConfig = new Config();
MemberAttributeConfig memberAttributes = hazelcastConfig.getMemberAttributeConfig();
memberAttributes.setAttribute("class-provider", "true");

HazecastInstance instance = Hazelcast.newHazelcastInstance(hazelcastConfig);