Upgrade Elasticsearch to 9.4.2

[ejsmith]

Summary

• upgrade active Elasticsearch, Kibana, Elastic APM, Docker Compose, sample, AppHost, Helm, and ECK references from 8.19.15 to 9.4.2
• add the custom Elasticsearch 9.4.2 image with mapper-size and a dedicated multi-architecture publishing workflow
• retain the 8.19.15 image/workflow as the supported major-upgrade source, but move the latest tag to the 9.x workflow
• make AppHost ports, image tag, container names, and data volume configurable so upgrade testing can run beside shared worktree infrastructure
• wait for yellow cluster health before declaring Elasticsearch ready, closing the recovered-shard startup race found during the persisted-volume rehearsal

Why

9.4.2 is the current Elastic Stack release and includes critical and security fixes. Elastic documents 8.19.x as the supported starting point for upgrades to 9.1.0 and later, and documents 8.x clients as compatible with 9.x through REST API compatibility.

• Elastic Stack 9.4.2 release notes
• Elastic upgrade paths and client compatibility
• ECK upgrade procedure
• Elasticsearch breaking changes

Compatibility and migration

• Exceptionless currently resolves Elastic.Clients.Elasticsearch 8.19.23 through Foundatio.Repositories; the 8.x client is supported against Elasticsearch 9.x
• repository ECK setup is already on 3.3.2, satisfying Elastic's ECK 3.x requirement for Stack 9.x
• the 8.19.15 custom image remains available for the supported 8.19.x → 9.4.2 upgrade path
• the 9.4.2 mapper-size plugin installed and loaded successfully
• Elasticsearch's 9.4.2 deprecation API returned no findings for the exercised data
• no Exceptionless public API, configuration key, serialization contract, or storage format is removed

Validation

• full backend suite against isolated Elasticsearch 9.4.2 on port 9210: 2,519 passed, 2 skipped, 0 failed
• clean 8.19.15 data volume upgraded to 9.4.2; first-start repository tests passed (8 passed, 1 expected skip)
• full Aspire stack ran healthy with isolated Elasticsearch/Kibana 9.4.2 on 9210/5610 while shared 8.19.15 services remained on 9200/5601
• Elasticsearch 9.4.2 reported a green cluster and indexed sample Exceptionless data without Elasticsearch warnings, errors, or deprecation entries
• Docker Compose configuration validation passed for development, deployment, APM, and standard sample stacks
• all changed workflow, Compose, Kubernetes, and Helm YAML parsed successfully
• focused dotnet format --verify-no-changes passed for the changed C# files
• GitHub API, client, E2E, application Docker, Elasticsearch 8.x image, and Elasticsearch 9.x image checks passed
• the first API attempt began 35 seconds before the new 9.4.2 image finished publishing and timed out waiting for Elasticsearch; the clean rerun passed in 9m32s once the image was available

Rollout risk

This is a major-version infrastructure upgrade. Elasticsearch cannot downgrade an upgraded data volume, so production rollout still requires a current snapshot and the Elastic Upgrade Assistant/pre-upgrade checks before applying the ECK manifest changes.

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[github-actions]

Package	Line Rate	Branch Rate	Complexity	Health
Exceptionless.Core	73%	66%	9587	➖
Exceptionless.AppHost	37%	37%	168	❌
Exceptionless.Insulation	37%	35%	286	❌
Exceptionless.Web	84%	67%	6935	✔
Summary	77% (22860 / 29808)	65% (10512 / 16054)	16976	✔