Unable to create a Knowledge Base with an existing OpenSearch collection

[gixproject]

Hi there!

Seems there is no way to use an existing OpenSearch collection. At least, no mentions of how to do that properly.

Description

There is no proper way to create a Knowledge Base with an existing OpenSearch Collection.
I've created a standalone OpenSearch collection with a correct name and security policies because collection_name is completely ignored while creating security policies (create_default_kb).

Configuration

I have the existing OpenSearch collection that I want to reuse, so I tried this setup:

resource "aws_iam_role" "bedrock_kb_role" {
  name = "AWSBedrockKBRole"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Effect = "Allow"
        Principal = {
          Service = "bedrock.amazonaws.com"
        }
        Action = "sts:AssumeRole"
      }
    ]
  })
}

module "knowledge_base" {
  source  = "aws-ia/bedrock/aws"
  version = "0.0.29"

  # Knowledge base configuration
  kb_type                  = "VECTOR"
  create_kb_log_group      = true
  create_kb                = true
  # kb_role_arn              = aws_iam_role.bedrock_kb_role.arn
  create_opensearch_config = true
  kb_storage_type             = "OPENSEARCH_SERVERLESS"

  use_existing_s3_data_source = true
  kb_s3_data_source           = module.data_bucket.s3_bucket_arn

  collection_arn  = module.opensearch_serverless.arn
  collection_name = module.opensearch_serverless.name

  create_vector_ingestion_configuration = true
  number_of_replicas                    = 1

  kb_name                        = "compatibility_kb"
  kb_description                 = "This knowledge base is designed to help you with compatibility questions."
  kb_embedding_model_arn         = "arn:aws:bedrock:eu-west-1::foundation-model/amazon.titan-embed-text-v2:0"
  kb_log_group_retention_in_days = 90

  # Agent configuration
  create_agent      = true
  foundation_model  = "anthropic.claude-sonnet-4-20250514-v1:0"
  instruction       = local.ai_agent_instructions
  agent_name        = "compatibility-agent"
  agent_description = "This agent is designed to help you with compatibility questions."
  # idle_session_ttl could be set to 1 hour to keep chat history active
}

Errors

I have different issues depending on whether a Knowledge Base (kb_role_arn) role is configured or not.

Without existing role (kb_role_arn is null), I've got this one:

With the existing role:

If you know how to create a Knowledge Base with an existing collection, please let me know 🙏🏻
I believe that it should be easy and unified. Thanks in advance!