OpenSearch Service Software Update Stuck in Initialization State since 24 hours

I understand your OpenSearch Service domain has been stuck in the "Initializing" state during a service software update for over 24 hours, which is preventing you from making any configuration changes.

Unfortunately, once an upgrade or update has been initiated in OpenSearch Service, it cannot be cancelled. OpenSearch Service uses a blue/green deployment process for domain upgrades and updates, and if the process gets stuck, you must wait for AWS to resolve the underlying issue before it can complete.

During the blue/green deployment process, several factors can cause the domain to get stuck in a processing state, including:

• Issues with shard relocation
• Large shard sizes
• High index or search load on the domain
• Insufficient disk space
• Reaching shard count quotas

To help monitor the situation while waiting for resolution, you can:

• Use Amazon CloudWatch to check OpenSearch Service metrics such as "FreeStorageSpace," "ClusterStatus," and "ClusterIndexWritesBlocked"
• Monitor the shard migration process using the "_cat/recovery" command if accessible

Since you've been stuck for over 24 hours and cannot cancel the operation, I recommend opening a support case with AWS Support immediately. They will need to investigate the underlying issue causing the update to remain stuck and can take the necessary actions to resolve it. When opening the case, provide all the details you've mentioned including the domain name, region, and the exact time the update was initiated.

In the future, to help prevent similar issues, consider initiating updates during periods of low cluster usage and ensuring your domain has sufficient resources to handle the increased load during an update.
Sources
Troubleshoot stuck or failed upgrades in OpenSearch Service | AWS re:Post