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https://issues.apache.org/jira/browse/YARN-8638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16590412#comment-16590412
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Eric Badger commented on YARN-8638:
-----------------------------------
bq. Default's logic is as before, but since pluggable runtimes get a chance to
intercept before default, isRuntimeRequested() will only get called in the same
circumstances where the original logic was. Is there a better implementation
for isRuntimeRequested()?
Yes, this is definitely backwards compatible and as is everything works as we
want it to. But in future development, if someone were to use this method, they
would assume that calling {{isRuntimeRequested()}} on the default runtime would
let them know if that's the runtime that was requested. With this logic, that
is not true. IMO, {{isRuntimeRequested()}} should be able to tell you
standalone whether that runtime is requested or not. If we want to shortcut it
by using the fall-through logic of the if statements, that's fine. But then I
would just say not to call this method and have the method be true to its name.
In reality, once this patch goes in, default runtime is only requested if we
don't ask for Docker _and_ we don't ask for a pluggable runtime.
> Allow linux container runtimes to be pluggable
> ----------------------------------------------
>
> Key: YARN-8638
> URL: https://issues.apache.org/jira/browse/YARN-8638
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: nodemanager
> Affects Versions: 3.2.0
> Reporter: Craig Condit
> Assignee: Craig Condit
> Priority: Minor
> Attachments: YARN-8638.001.patch, YARN-8638.002.patch
>
>
> YARN currently supports three different Linux container runtimes (default,
> docker, and javasandbox). However, it would be relatively straightforward to
> support arbitrary runtime implementations. This would enable easier
> experimentation with new and emerging runtime technologies (runc, containerd,
> etc.) without requiring a rebuild and redeployment of Hadoop.
> This could be accomplished via a simple configuration change:
> {code:xml}
> <property>
> <name>yarn.nodemanager.runtime.linux.allowed-runtimes</name>
> <value>default,docker,experimental</value>
> </property>
>
> <property>
> <name>yarn.nodemanager.runtime.linux.experimental.class</name>
> <value>com.somecompany.yarn.runtime.ExperimentalLinuxContainerRuntime</value>
> </property>{code}
>
> In this example, {{yarn.nodemanager.runtime.linux.allowed-runtimes}} would
> now allow arbitrary values. Additionally,
> {{yarn.nodemanager.runtime.linux.\{RUNTIME_KEY}.class}} would indicate the
> {{LinuxContainerRuntime}} implementation to instantiate. A no-argument
> constructor should be sufficient, as {{LinuxContainerRuntime}} already
> provides an {{initialize()}} method.
> {{DockerLinuxContainerRuntime.isDockerContainerRequested(Map<String, String>
> env)}} and {{JavaSandboxLinuxContainerRuntime.isSandboxContainerRequested()}}
> could be generalized to {{isRuntimeRequested(Map<String, String> env)}} and
> added to the {{LinuxContainerRuntime}} interface. This would allow
> {{DelegatingLinuxContainerRuntime}} to select an appropriate runtime based on
> whether that runtime claimed ownership of the current container execution.
> For backwards compatibility, the existing values (default,docker,javasandbox)
> would continue to be supported as-is. Under the current logic, the evaluation
> order is javasandbox, docker, default (with default being chosen if no other
> candidates are available). Under the new evaluation logic, pluggable runtimes
> would be evaluated after docker and before default, in the order in which
> they are defined in the allowed-runtimes list. This will change no behavior
> on current clusters (as there would be no pluggable runtimes defined), and
> preserves behavior with respect to ordering of existing runtimes.
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