HDDS-13138. [Docs] Update Topology Awareness user doc.

[jojochuang]

What changes were proposed in this pull request?

HDDS-13138. [Docs] Update Topology Awareness user doc.

Please describe your PR in detail:

• Couple of things to update in the doc: default placement policy is changed.
• additional placement policies: SCMContainerPlacementCapacity
• Erasure Coding placement policy: SCMCommonPlacementPolicy

Generated-by: Google Gemini 2.5 Pro (Preview) Deep Research, with the prompt:

I want to update the Ozone's Topology Awareness user doc: https://ozone.apache.org/docs/edge/feature/topology.html

First, look at the resources online and Ozone source code, and find out any stale content in the user doc. Find new placement policies not mentioned in the doc. Find out what they do and provide examples to illustrate how they work. Best practices.

Second, update the doc based on the new information incorporated.

Third, incorporate placement policy for Ozone Erasure Coding. Look at Ozone source code and design doc as source of truth.

and then updated the doc manually.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-13138

How was this patch tested?

User doc only.

[Copilot]

Pull Request Overview

This PR updates the Topology Awareness user documentation for Apache Ozone by revising outdated content and incorporating new placement policies.

• Updated descriptions of topology-aware operations including both static and dynamic mapping.
• Introduced new sections detailing the additional placement policies for both RATIS and Erasure Coded (EC) containers.
• Revised configuration examples and best practice guidelines for network topology and container placements.

Comments suppressed due to low confidence (2)

hadoop-hdds/docs/content/feature/Topology.md:57

• Ensure that the updated topology mapping file path (/etc/ozone/topology.map) is consistent with deployment standards and accurately documented.

<value>/etc/ozone/topology.map</value>

hadoop-hdds/docs/content/feature/Topology.md:81

• Confirm that the updated script path for dynamic rack mapping (/etc/ozone/determine_rack.sh) aligns with current deployment configurations and file system conventions.

<value>/etc/ozone/determine_rack.sh</value>

[ChenSammi]

Gemini produces the content, and Copilot reviews the content. We are really into a new era :)

[ChenSammi]

I believe this is not true, pipeline creation considers topology.

[jojochuang]

hdds.scm.pipeline.choose.policy.imp default is RandomPipelineChoosePolicy, same for EC: hdds.scm.ec.pipeline.choose.policy.impl.

/**
 * Random choose policy that randomly chooses pipeline.
 * That are we just randomly place containers without any considerations of
 * utilization.
 */
public class RandomPipelineChoosePolicy implements PipelineChoosePolicy {

[ChenSammi]

RandomPipelineChoosePolicy is to choose which pipeline to use if there are multiple qualified pipelines.

What I mean is RAFT pipeline creation, during RAFT pipeline creation, it do consider topology.

PipelinePlacementPolicy#chooseDatanodesInternal
// Randomly picks nodes when all nodes are equal or factor is ONE.
    // This happens when network topology is absent or
    // all nodes are on the same rack.
    if (checkAllNodesAreEqual(nodeManager.getClusterNetworkTopologyMap())) {
      return super.getResultSet(nodesRequired, healthyNodes);
    } else {
      // Since topology and rack awareness are available, picks nodes
      // based on them.
      return this.getResultSetWithTopology(nodesRequired, healthyNodes,
          usedNodes);
    }

[jojochuang]

Got it. good to know.

[ChenSammi]

Thanks @jojochuang , I have reviewed the RATIS part. For the EC part, it's better to have someone familiar with EC implementation to have a look.

[jojochuang]

I'd like to add pipeline choosing policy such as https://issues.apache.org/jira/browse/HDDS-9345
-but maybe in another jira.-

Edit: added them. It was super easy to add using GitHub Copilot Agent

[jojochuang]

Ok I removed the EC section in the doc. Will commit with just the Ratis related changes, and leave the EC topology awareness to a subtask: HDDS-13575

[jojochuang]

Thanks @ChenSammi I will raise another PR for the EC doc.