(aws-diagram-mcp-server):Diagram generation fails with "Diagram file was not created" error when using multiple connections

[gunhee1314]

Describe the bug

The awslabs.aws-diagram-mcp-server fails to generate diagrams when the number of connections between nodes
exceeds approximately 5-6 connections. The tool returns a generic error message "Diagram file was not created.
Check your code for errors" without providing specific details about what caused the failure.

Expected Behavior

The diagram generation should work with a reasonable number of connections (10-15+ connections) as shown in
existing examples and documentation. Complex AWS architectures typically require multiple connections to
accurately represent the relationships between services.

Current Behavior

• ✅ Works: Simple diagrams with 1-5 connections
• ❌ Fails: Diagrams with 6+ connections
• ❌ Fails: Cross-cluster connections (connections between nodes in different clusters)
• ❌ Fails: Complex connection patterns

Error message received:
{
"status": "error",
"path": null,
"message": "Diagram file was not created. Check your code for errors."
}

Reproduction Steps

Working example (5 connections):

python
with Diagram("Working Example", show=False, direction="TB", graph_attr={"size": "6,8!"}):
    users = User("Users")
    alb = ALB("ALB")
    web_2a = EC2("Web 2a")
    web_2c = EC2("Web 2c")
    was_2a = EC2("WAS 2a")
    was_2c = EC2("WAS 2c")

    # 5 connections - WORKS
    users >> alb
    alb >> web_2a
    alb >> web_2c
    web_2a >> was_2a
    web_2c >> was_2c

Failing example (7 connections):

python
with Diagram("Failing Example", show=False, direction="TB", graph_attr={"size": "6,8!"}):
    users = User("Users")
    alb = ALB("ALB")
    web_2a = EC2("Web 2a")
    web_2c = EC2("Web 2c")
    was_2a = EC2("WAS 2a")
    was_2c = EC2("WAS 2c")
    rds_2a = RDS("RDS 2a")
    rds_2c = RDS("RDS 2c")

    # 7 connections - FAILS
    users >> alb
    alb >> web_2a
    alb >> web_2c
    web_2a >> was_2a
    web_2c >> was_2c
    was_2a >> rds_2a
    was_2c >> rds_2c

Cross-cluster connection failure:

python
with Diagram("Cross-cluster Failure", show=False, direction="TB"):
    users = User("Users")

    with Cluster("Load Balancers"):
        alb = ALB("ALB")

    with Cluster("Web Servers"):
        web = EC2("Web")

    # Cross-cluster connection - FAILS
    users >> alb  # Works (external to cluster)
    alb >> web    # FAILS (cluster to cluster)

Possible Solution

No response

Additional Information/Context

No response

OS

macOS

Server

aws-diagram-mcp-server

Server Version

No response

Region experiencing the issue

ap-northeast-2

Other information

• Installation method: uvx
• Python environment: Default system Python with uvx

Service quota

• I have reviewed the service quotas for this construct