arjunmohnot opened a new pull request, #7049:
URL: https://github.com/apache/hadoop/pull/7049
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### Description of PR
#### 1. Overview
When the ResourceManager starts, nodes listed in the "include" file are not
immediately reported until their corresponding NodeManagers send their first
heartbeat. However, nodes in the "exclude" file are instantly reflected in the
"Decommissioned Hosts" section with a port value of -1.
#### 2. Challenges
1. **Untracked NodeManagers**: During Resourcemanager HA failover or RM
standalone restart, some nodes may not report back, even though they are listed
in the _"include"_ file. These nodes neither appear in the _LOST_ state nor are
they represented in the RM's JMX metrics. This results in an untracked state,
making it difficult to monitor their status. While in HDFS similar behaviour
exists and datanodes are marked as _"DEAD"_.
2. **Monitoring Gaps**: Nodes in the "include" file are not visible until
they send their first heartbeat, impacting real-time cluster monitoring when
being dependent on cluster metrics sink.
3. **Operational Impact**: Unreported nodes cause operational difficulties,
particularly in automated workflows such as OS Upgrade Automation (OSUA), node
recovery automation, etc. requiring workarounds to determine accurate status
for nodes that don't report.
#### 3. Proposed Solution
To address these issues, the code automatically assigns the **_LOST_** state
to nodes listed in the _"include"_ file that are not registered and not part of
the exclude file at RM startup or during HA failover. This is indicated by a
special port value of **-2**, marking the node as LOST but not yet reported.
Once a heartbeat is received for that node, it will transition from LOST to
RUNNING, UNHEALTHY, or any other desired state.
#### 4. Key Implementation Points
1. **Mark Unreported Nodes as LOST**:
- **Class Modified**: `NodesListManager`
- **Method**: `refreshHostsReader`
- **Functionality**:
- Automatically marks nodes listed in the **"include"** file as
**LOST** if they are not part of the RM active node context.
- For non-HA setups, this process is triggered during **RM service
startup**, ensuring unregistered nodes are initially set to **LOST**.
- Port value **-2** indicates that the node is untracked.
2. **Handle Node Heartbeat and Transition**:
- **Class Modified**: `RMNodeImpl`
- **Method**: State transition method
- **Functionality**:
- Upon receiving the first heartbeat from a node, the system checks if
the node exists in the **LOST** state (If nodeID has -2 port for that host) by
verifying against `getInactiveRMNodes()`.
- If the node is found in the **LOST** state:
- Remove the node from the inactive node list.
- Remove the node from the active node list to register it with a
new nodeID having its required port.
- Maintain the hostname in the RM context for proper host tracking.
- Decrement the count of **LOST** nodes.
- Re-register the node with the new nodeID and transition it back to
the active node set, ensuring it recovers gracefully from the **LOST** state.
- This logic ensures a smooth transition for nodes from **NEW** to
**LOST** and back to active upon heartbeat reception.
#### 5. Flow Diagram
```yaml
+---------------------------+
| RM Startup / HA Failover |
+---------------------------+
|
v
Check Nodes in RM Context
|
+-----------------------------+
| |
Not Registered & Not in Registered or in
Exclude File Exclude File
| |
v v
Mark Node as LOST (port -2) Node processed normally
|
v
Wait for Heartbeat
|
v
Receive Heartbeat
|
v
Node State Check
|
+------------------------------------v
| |
Previous NodeID Removed Same Hostname
With Port -2 Still Remains in the RM Context
| |
| |
v |
[No Further Transition] |
|
|
Handle Node Re-Registration -----------+
|
v
New NodeID (Same Hostname + New Registered Port)
|
v
+-----------------------+
| Transition to |
| ACTIVE/RUNNING |
+-----------------------+
```
#### 6. Additional Considerations
- **Feature Flag Control**: This feature can be enabled/disabled via a
configuration flag (default: False).
```bash
<property>
<name>yarn.resourcemanager.enable-tracking-for-unregistered-nodes</name>
<value>false</value>
</property>
```
### How was this patch tested?
- The implementation has been tested on multiple environments both in non-HA
and HA setups. A dummy Docker-based
[setup](https://github.com/arjunmohnot/hadoop-yarn-docker/tree/main) has been
created to replicate the behavior, and bare metal HA setup with Zookeeper was
used to validate the failover scenario between HA1 and HA2 RM node.
- Added the required unit test cases that passes with the modified code.
```bash
[INFO] -------------------------------------------------------
[INFO] T E S T S
[INFO] -------------------------------------------------------
[INFO] Running
org.apache.hadoop.yarn.server.resourcemanager.TestResourceTrackerService
[INFO] Tests run: 47, Failures: 0, Errors: 0, Skipped: 0, Time elapsed:
80.975 s - in
org.apache.hadoop.yarn.server.resourcemanager.TestResourceTrackerService
[INFO]
[INFO] Results:
[INFO]
[INFO] Tests run: 47, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO]
------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO]
------------------------------------------------------------------------
[INFO] Total time: 02:10 min
[INFO] Finished at: 2024-09-16T20:31:18+05:30
[INFO]
------------------------------------------------------------------------
```
- Build and code compilation also succeeded.
```bash
[INFO]
------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO]
------------------------------------------------------------------------
[INFO] Total time: 29:27 min
[INFO] Finished at: 2024-09-16T21:25:07+05:30
[INFO]
------------------------------------------------------------------------
```
- Reference Logs:
- Event dispatch to mark the qualified unregistered nodes as LOST:
```bash
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:427) - Lost node: nodemanager2
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:427) - Lost node: nodemanager1
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:427) - Lost node: nodemanager3
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:491) - Successfully dispatched LOST event and
deactivated node: nodemanager2, Node ID: nodemanager2:-2
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:491) - Successfully dispatched LOST event and
deactivated node: nodemanager1, Node ID: nodemanager1:-2
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:491) - Successfully dispatched LOST event and
deactivated node: nodemanager3, Node ID: nodemanager3:-2
2024-09-16 17:16:28,550 INFO resourcemanager.NodesListManager
(NodesListManager.java:438) - Successfully marked unregistered nodes as LOST
2024-09-16 17:16:28,552 INFO rmnode.RMNodeImpl (RMNodeImpl.java:1232) -
Deactivating Node nodemanager2:-2 as it is now LOST
2024-09-16 17:16:29,278 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager2:-2 Node Transitioned from NEW to LOST
2024-09-16 17:16:29,278 INFO rmnode.RMNodeImpl (RMNodeImpl.java:1232) -
Deactivating Node nodemanager1:-2 as it is now LOST
2024-09-16 17:16:30,068 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager1:-2 Node Transitioned from NEW to LOST
2024-09-16 17:16:30,069 INFO rmnode.RMNodeImpl (RMNodeImpl.java:1232) -
Deactivating Node nodemanager3:-2 as it is now LOST
2024-09-16 17:16:30,778 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager3:-2 Node Transitioned from NEW to LOST
```
- Once the heartbeat is received it re-registers the hostname and mark
them to the running state:
```bash
2024-09-16 17:17:12,672 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager1:38065 Node Transitioned from NEW to RUNNING
2024-09-16 17:17:12,673 INFO capacity.CapacityScheduler
(CapacityScheduler.java:2249) - Added node nodemanager1:38065 clusterResource:
<memory:16384, vCores:16>
2024-09-16 17:17:12,732 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager2:40107 Node Transitioned from NEW to RUNNING
2024-09-16 17:17:12,734 INFO capacity.CapacityScheduler
(CapacityScheduler.java:2249) - Added node nodemanager2:40107 clusterResource:
<memory:24576, vCores:24>
2024-09-16 17:17:12,262 INFO rmnode.RMNodeImpl (RMNodeImpl.java:785) -
nodemanager3:39725 Node Transitioned from NEW to RUNNING
2024-09-16 17:17:12,265 INFO capacity.CapacityScheduler
(CapacityScheduler.java:2249) - Added node nodemanager3:39725 clusterResource:
<memory:8192, vCores:8>
```
- Reference screenshots and video to show LOST nodes, and active nodes state
transition after the NM re-registration (Note NMs were automatically marked as
lost even though its initial heartbeat was not registered at the time of RM
startup):
<img width="1726" alt="Unregistered lost nodes"
src="https://github.com/user-attachments/assets/796df3b5-78b1-4ce8-98d4-f65ef23d5e13";>
<img width="1724" alt="Nodes transitioned from lost to active"
src="https://github.com/user-attachments/assets/0b995e92-d47b-43f1-8398-69de781bf5b7";>
https://github.com/user-attachments/assets/c8bbe1c7-ddb6-4ba9-bdf3-1d92be908f51
### For code changes:
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- [ ] If adding new dependencies to the code, are these dependencies
licensed in a way that is compatible for inclusion under [ASF
2.0](http://www.apache.org/legal/resolved.html#category-a)?
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`NOTICE-binary` files?
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