The 'describe-instances' is a very power CLI/API call that returns a detailed dataset about every single EC2 instance in your account. However, chances are that you have more than just a handful of instances in your account so when you run this call in its default form like this
aws ec2 describe-instances --output tableThe amount of data get returned back will make it difficult to consume. Luckily, AWS CLI has built-in --filter and --query switches that can help you keep your result set nice, clean and manageable. Following example shows how to filter out your instances by a specific "tag" using wildcards, and display only the fields that you really care about
aws ec2 describe-instances --filter "Name=tag:Name, Values=blue-*" --query 'Reservations[*].Instances[*].{ID:InstanceId, Name:PrivateDnsName}' --output text --output table
The above command will filter out all the EC2 instances that have a tag, "Name" set to the value "blue-*", (notice the use of wildcard in the value. Here is the result of running the above command
------------------------------------------------
| DescribeInstances |
+-------------+--------------------------------+
| ID | Name |
+-------------+--------------------------------+
| i-62xcbxxx | ip-172-16-1-xxx.ec2.internal |
| i-63xcbxxx | ip-172-16-1-xxx.ec2.internal |
| i-6fxcbxxx | ip-172-16-1-xxx.ec2.internal |
| i-6excbxxx | ip-172-16-1-xxx.ec2.internal |
+-------------+--------------------------------+
Also sometimes you want to display as sepcific tag in the output, this command below will accomplish that. I am looking for a way to make it a bit cleaner so there is one record per row, but for this works
aws ec2 describe-instances --query "Reservations[].Instances[].[InstanceId,Tags[?Key=='Name'].Value]" --output table