I'm configuring AWS ECS service autoscaling. When I try to load my service, an alarm executes an action to create a new task. But in the service tab 'Tasks' I can't see a new task. But 'Desired count' value still increases. Does it mean that a new task is created or not?
The desired count is the count of the task by your service at that moment. That does not essentially means that your all that's will be in running state.
Let me quote from AWS doc.
Your Amazon ECS service can optionally be configured to use Service Auto Scaling to adjust its desired count up or down in response to CloudWatch alarms. Service Auto Scaling leverages the Application Auto Scaling service to provide this functionality.
Ref: https://docs.aws.amazon.com/AmazonECS/latest/developerguide/service-auto-scaling.html
There might be 2 situations.
Your task might be in stopped because of multiple reasons with your application. You can see the task status under the services section.
Your task was not able to run because of the insufficient underlying container instance resources if you are using EC2 Type in the cluster.
I suggest you check events sections of the services and let me know what exact information you are able to see there.
ECS -> Cluster Name -> Service Name -> Event Tab