SOLR-17949: Add Azure Blob Storage backup repository module

[prateeksinghalgit]

Implements Azure Blob Storage backup repository as discussed in SOLR-17949.

Description

This PR adds a new backup repository implementation for Azure Blob Storage, enabling Solr collections to be backed up to and restored from Microsoft Azure.

Key Features:

• Full backup/restore functionality to Azure Blob Storage
• Support for 4 authentication methods (Connection String, Account Key, SAS Token, Azure Identity)
• Incremental backup support with versioning
• Data integrity verification (checksum validation)
• Compatible with Azurite emulator for local testing
• Comprehensive documentation and 76 passing unit tests

Solution

The implementation follows Solr's BackupRepository interface pattern, similar to existing S3 and GCS repository modules:

• AzureBlobBackupRepository: Main class implementing Solr's BackupRepository interface
• AzureBlobStorageClient: Wrapper for Azure SDK, providing file operations
• AzureBlobIndexInput: Custom Lucene IndexInput for reading from Azure blobs
• AzureBlobOutputStream: Custom output stream for writing to Azure blobs
• Authentication: Supports 4 methods via flexible configuration in solr.xml

All streaming operations are compatible with Solr's ResumableInputStream for fault-tolerant transfers.

Implementation stats:

• 8 implementation files (1,606 LOC)
• 8 test files (2,180 LOC)
• All dependencies Apache 2.0 licensed

Tests

Unit Tests: 76/76 passing (100%)

./gradlew :solr:modules:blob-repository:test
# Result: BUILD SUCCESSFUL - 76 test(s)

Test Coverage:

• Basic read/write operations
• Large file handling (1GB+)
• Binary data integrity
• Concurrent operations
• Stream lifecycle (close/resume behavior)
• Incremental backups
• All 4 authentication methods
• Integration with Azurite (local emulator)
• Integration with real Azure Blob Storage

Testing Instructions:
Can be tested locally with Azurite emulator (no Azure account needed) or with real Azure Blob Storage. See solr/modules/blob-repository/README.md for detailed setup instructions.

Checklist

Please review the following and check all that apply:

• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
• I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
• I have developed this patch against the main branch.
• I have run ./gradlew :solr:modules:blob-repository:check (module-specific check passed).
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[pratsgit]

Quick update: following up on the dev@ thread.

To clarify scope — although the diff is large, the actual implementation is centered in 8 main files and 8 test files; the rest are license header updates.

Happy to split the PR into smaller logical chunks (core module / tests / docs) if that helps with review.

Thanks everyone!

[janhoy]

Don’t have time to review but asked copilot for an opinion 😉

[janhoy]

Only immediate comment is naming. «Blob-repository» is too generic. Should contain word «azure»?

[Copilot]

Pull Request Overview

This PR implements Azure Blob Storage backup repository support for Apache Solr, enabling collections to be backed up to and restored from Microsoft Azure. The implementation follows established patterns from existing S3 and GCS modules, providing 4 authentication methods (Connection String, Account Key, SAS Token, Azure Identity), incremental backup support, and comprehensive documentation with 76 passing unit tests.

Reviewed Changes

Copilot reviewed 70 out of 70 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
backup-restore.adoc	Adds comprehensive documentation for BlobBackupRepository with authentication methods and configuration
BlobBackupRepository.java	Main repository implementation following Solr's BackupRepository interface
BlobStorageClient.java	Azure SDK wrapper providing blob storage operations
BlobOutputStream.java	Custom output stream for block-based blob uploads
BlobIndexInput.java	Lucene IndexInput implementation with page caching
Test files	8 test classes with 76 passing tests covering all functionality
build.gradle	Module build configuration with Azure SDK dependencies
License files	License and notice files for Azure and Netty dependencies

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[prateeksinghalgit]

Only immediate comment is naming. «Blob-repository» is too generic. Should contain word «azure»?

made the change to azure-blob-repository

[janhoy]

I'll leave the rest of the review to others more proficient in Azure Blob than me (have never used it). I'd love to test it with a read AzBlob but I'll leave that to someone who already have an active account.

I have a concern that the PR feels largely AI generated(?), lacking the care to details that we require for contributions. Have me excused @prateeksinghalgit if this is not correct, it was just a hunch I got while reviewing. I'd rather have a short well thought out README with useful advice for users than three pages of detailed step by step instructions for testing and developing the feature.

For other reviewers to pick up where I left, consider in partifular the HTTP client choice, correct licensing and avoiding hard coded ports in tests. I have not done a complete review, not read the ref-guide part at all, just commented on things me and Copilot saw immediately.

[pratsgit]

Hi all,

I’ve pushed a set of updates based on the feedback so far:

1. Switched the integration tests to use Testcontainers with Azurite (no hard-coded ports / external prereqs) and disabled the Security Manager for this module’s tests, following the pattern used in the extraction module.
2. Addressed HTTP client concerns by using azure-core-http-okhttp and keeping those deps in test scope only, plus explicit test deps.
3. Cleaned up and significantly shortened the README and docs
4. Did additional cleanup to align naming, structure, and configuration patterns with those of the existing repository plugins.

Please let me know if anything else should be adjusted that would help move the review forward.

Happy to make further changes.

Thanks again for the thoughtful review and guidance so far!

— Prateek

[prateeksinghalgit]

Hi All,

I’ve fixed the recent CI failures:

1. Added proper thread leak filters for Testcontainers / JNA so tests are cleanly skipped when Docker isn’t available in CI.
2. Fixed two error-prone findings (IntLongMath and MissingOverride) that only surfaced in CI because error-prone is disabled by default in local builds unless -Pvalidation.errorprone=true is used.

Please let me know if anything else should be adjusted to help move the review forward. I’m happy to iterate further as needed.

[github-actions]

This PR has had no activity for 60 days and is now labeled as stale. Any new activity will remove the stale label. To attract more reviewers, please tag people who might be familiar with the code area and/or notify the dev@solr.apache.org mailing list. To exempt this PR from being marked as stale, make it a draft PR or add the label "exempt-stale". If left unattended, this PR will be closed after another 60 days of inactivity. Thank you for your contribution!

[prateeksinghalgit]

Thanks @janhoy for adding more reviewers. @HoustonPutman and @psalagnac ,let me know if you have any questions related to the pr.

[psalagnac]

Thanks for adding me as a reviewer.
I've been pretty busy recently and I haven't got the chance to do the review yet. I'll try to do a complete review before end of next week.