Lets start with simple example …

We have the following EC2 instances in AWS Account:

Search for the term ‘TEST-NODE’ yields the same results as searching for ‘test-node’ in the AWS Web interface.

Searching for ‘TEST-NODE':

Searching for ‘test-node':

… it behaves the same way. It is case-insensitive.

However, commend line tools will produce totally different output.

Searching for ‘TEST-NODE':

:~> aws ec2 describe-instances --filters "Name=tag:Name,Values=*TEST-NODE*" --query 'Reservations[*].Instances[*].Tags[?Key==`Name`].Value[]' --output text
TEST-NODE-1
:~>

Searching for ‘test-node':

:~> aws ec2 describe-instances --filters "Name=tag:Name,Values=*test-node*" --query 'Reservations[*].Instances[*].Tags[?Key==`Name`].Value[]' --output text
test-node-5
:~>

Python + Boto shows the same behavior (not surprisingly, AWS CLI uses Boto):

Searching for ‘TEST-NODE':

:~> python
Python 2.7.5 (default, Mar  9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import boto
>>> import boto.ec2
>>> conn = boto.ec2.connect_to_region('us-east-1', aws_access_key_id='', aws_secret_access_key='')
>>> reservations = conn.get_all_instances(filters = {'instance-state-name' : 'running', "tag:Name": "*" + 'TEST-NODE' + "*"})
>>> for r in reservations:
...     for i in r.instances:
...             print i.tags['Name']
...
TEST-NODE-1
>>> ^D
:~>

Searching for ‘test-node':

:~> python
Python 2.7.5 (default, Mar  9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import boto
>>> import boto.ec2
>>> conn = boto.ec2.connect_to_region('us-east-1', aws_access_key_id='', aws_secret_access_key='')
>>> reservations = conn.get_all_instances(filters = {'instance-state-name' : 'running', "tag:Name": "*" + 'test-node' + "*"})
>>> for r in reservations:
...     for i in r.instances:
...             print i.tags['Name']
...
test-node-5
>>> ^D
:~>

Moral of the story: ALWAYS VERIFY/ENFORCE THAT DATA IS PROPERLY FORMATTED!

There are multiple possible solutions to this issue. With the cost of few extra cycles one can make sure proper comparison is implemented:

:~> python
Python 2.7.5 (default, Mar  9 2014, 22:15:05)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import boto
>>> import boto.ec2
>>> conn = boto.ec2.connect_to_region('us-east-1', aws_access_key_id='', aws_secret_access_key='')
>>> reservations = conn.get_all_instances(filters = {'instance-state-name' : 'running'})
>>> for r in reservations:
...     for i in r.instances:
...             if 'test-node'.upper() in i.tags['Name'].upper():
...                     print i.tags['Name']
...
TEST-NODE-1
TEST-Node-2
TEST-node-3
test-node-5
>>> ^D
:~>

References

• http://docs.aws.amazon.com/cli/latest/reference/ec2/describe-instances.html