[BUG] issues otel_logs_source during upgrade from 2.13 to 2.14

[Sabo-kun]

Describe the bug
I tried to upgrade DataPrepper from 2.13 to 2.14 while keeping the same configuration but there was an exception preventing the pipelines from starting.

The issue involves the otel_logs_source i.e.:

2026-03-03T13:37:56,806 [otel-logs-pipeline-sink-worker-10-thread-1] ERROR org.opensearch.dataprepper.core.pipeline.common.PipelineThreadPoolExecutor - Pipeline [otel-logs-pipeline] process worker encountered a fatal exception, cannot proceed further
java.util.concurrent.ExecutionException: java.lang.NullPointerException: Cannot invoke "String.replace(java.lang.CharSequence, java.lang.CharSequence)" because the return value of "org.opensearch.dataprepper.plugins.source.otellogs.OTelLogsSourceConfig.getHttpPath()" is null
	at java.base/java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.base/java.util.concurrent.FutureTask.get(FutureTask.java:191)
	at org.opensearch.dataprepper.core.pipeline.common.PipelineThreadPoolExecutor.afterExecute(PipelineThreadPoolExecutor.java:75)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1137)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.lang.Thread.run(Thread.java:840)
Caused by: java.lang.NullPointerException: Cannot invoke "String.replace(java.lang.CharSequence, java.lang.CharSequence)" because the return value of "org.opensearch.dataprepper.plugins.source.otellogs.OTelLogsSourceConfig.getHttpPath()" is null
	at org.opensearch.dataprepper.plugins.source.otellogs.OTelLogsSource.configureHttpService(OTelLogsSource.java:180)
	at org.opensearch.dataprepper.plugins.source.otellogs.OTelLogsSource.createServer(OTelLogsSource.java:174)
	at org.opensearch.dataprepper.plugins.source.otellogs.OTelLogsSource.start(OTelLogsSource.java:118)
	at org.opensearch.dataprepper.core.pipeline.Pipeline.startSourceAndProcessors(Pipeline.java:251)
	at org.opensearch.dataprepper.core.pipeline.Pipeline.lambda$execute$5(Pipeline.java:302)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	... 2 more

To Reproduce

DataPrepper and Otel Collector are deployed both as containers in kubernetes

The same configuration template works if I use the following image (which matches 2.13.0 DataPrepper version)
image: opensearchproject/data-prepper@sha256:57c53434d040ee9fb4cf7224d75371ca2390cb36d29c9324025f8220a89eca8f

Steps to reproduce the behavior:

1. apply the following yaml files

apiVersion: v1
kind: ServiceAccount
metadata:
  name: opentelemetrysa
  namespace: default
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: dataprepper-pipeline-file
  namespace: default
data:
  pipelines.yaml: |
    # Minimal reproduction with file sink for persistent logs
    otel-logs-pipeline:
      source:
        otel_logs_source:
          port: 21892
          ssl: false
          # Bug: Missing http_path causes NullPointerException
      sink:
        - stdout:
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: dataprepper-file-sink
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: dataprepper-file-sink
  template:
    metadata:
      labels:
        app: dataprepper-file-sink
    spec:
      securityContext:
        runAsUser: 1000
        runAsNonRoot: True
        seccompProfile:
          type: RuntimeDefault
      serviceAccountName: opentelemetrysa

      containers:
        - name: dataprepper
          image: opensearchproject/data-prepper:2.14.0
          resources: {}
          securityContext:
            readOnlyRootFilesystem: false
            allowPrivilegeEscalation: false
            capabilities:
              drop: ["ALL"]
          ports:
            - containerPort: 21890
            - containerPort: 21891
            - containerPort: 21892
            - containerPort: 4900
          volumeMounts:
            - name: pipeline-config
              mountPath: /usr/share/data-prepper/pipelines
            - name: logs-output
              mountPath: /tmp/dataprepper-logs
      volumes:
        - name: pipeline-config
          configMap:
            name: dataprepper-pipeline-file
        - name: logs-output
          emptyDir: {}
---
apiVersion: v1
kind: Service
metadata:
  name: dataprepper-file-sink
  namespace: default
spec:
  selector:
    app: dataprepper-file-sink
  ports:
    - name: otlp-traces
      port: 21890
      targetPort: 21890
    - name: otlp-metrics
      port: 21891
      targetPort: 21891
    - name: otlp-logs
      port: 21892
      targetPort: 21892
    - name: health
      port: 4900
      targetPort: 4900

2. check the logs

Expected behavior
The pipeline should work as earlier

[Sabo-kun]

Looking at the code, I noticed that the regression was introduced by the following line which wasn't properly protected:
configureHttpService(serverBuilder, buffer, executor.getQueue());
in this file:
data-prepper/data-prepper-plugins/otel-logs-source/src/main/java/org/opensearch/dataprepper/plugins/source/otellogs

It should be addressed by the release of this change:
26400a2
which checks that getHttpPath() is not null before to configure the httpService

[dlvenable]

@Sabo-kun , Yes, we will release a patch release with this fix.

[dlvenable]

Backport #6572 has this fix.