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aws-autodiscovery-templater
Auto discovery in AWS can be tricky for legacy applications. Due to time or complexity, it’s not always possible to write auto discovery code to let applications find each other in an elastic/scaling environment. Sometimes, listing the ips/hosts for hosts in a config file will be enough, and that’s what this script does.
Installation
Installation is simply
$ pip install aws-autodiscovery-templater
Usage
The easiest way is to use the included cli tool (although there is a small python library which you can use). This project uses the jinja2 templating engine, so you can find details there about how to write templates. The following variables are passed to the templating engine:
{ "private": { "ips": [...], "hostnames": [...] }, "public": { "ips": [...], "hostnames": [...] }, "reservations": { ... } }
The first two entries, contain an array of strings for public and private, ips and hostnames. The reservations entry contains the raw output from EC2.Client.describe_instances.
From this, we can create a template that looks like this
# /path/to/config.yaml {% if private['ips'] %} private_ips:{% for ip in private['ips'] %} - {{ ip }}{% endfor %}{% endif %}
We’ll be using this template in the following examples.
Note: Before you run any of this, you need to have either your AWS credentials set up in ~/.aws/{config,credentials}, or in AWS_* environment variables.
Example run
$ aws-autodiscovery-templater \ --template-path /path/to/config.yaml \ # Path to jina2 formatted template --profile my-aws-profile \ # AWS credentials as defined in ~/.aws/credentials --stdout \ # Print result to stdout --filter-empty # Don't include null/missing values (eg. not all machines have public IPs
Filtering instances
More importantly, you can filter instances based on their tags. This filter is a json objectstructured in the same manner as described in aws ec2 describe-instances, excluding the root ["Reservations"] key.
$ aws-autodiscovery-templater \ --template-path /path/to/config.yaml \ --profile my-aws-profile \ --stdout \ --filter-empty --filter "Name=tag:Application,Values=[mongodb,mongodb-master]" private_ips: - 10.0.0.20 - 10.0.0.10 - 10.0.0.30
Inline help:
# For more details, have a look at the --help option $ aws-autodiscovery-templater --help usage: aws-autodiscovery-templater [-h] [--aws-access-key-id AWS_ACCESS_KEY_ID] [--aws-secret-access-key AWS_SECRET_ACCESS_KEY] [--aws-session-token AWS_SESSION_TOKEN] [--region REGION] [--profile PROFILE] [--role ROLE] [--auth-debug] [--role-session-name ROLE_SESSION_NAME] --template-path TEMPLATE_PATH --stdout [--vpc-ids] [--filter FILTER] [--filter-empty] optional arguments: -h, --help show this help message and exit AWS credentials: --aws-access-key-id AWS_ACCESS_KEY_ID AWS access key --aws-secret-access-key AWS_SECRET_ACCESS_KEY Access and secret key variables override credentials stored in credential and config files --aws-session-token AWS_SESSION_TOKEN A session token is only required if you are using temporary security credentials. --region REGION This variable overrides the default region of the in- use profile, if set. --profile PROFILE This can be the name of a profile stored in a credential or config file, or default to use the default profile. --role ROLE Fully qualified role arn to assume --auth-debug Enter debug mode, which will print credentials and then exist at `create_session`. --role-session-name ROLE_SESSION_NAME If you have assigned a role, set a --role-session-name AWS Autodiscovery Templater: --template-path TEMPLATE_PATH Path to the template to fill variables into. --stdout Prints a json object containing the retrieves resources --vpc-ids Optionally restrict the filtering to a particular list of IPs. Comma seperated list of vpc-ids. --filter FILTER Filter for ec2 instances as defined in http://boto3.re adthedocs.org/en/latest/reference/services/ec2.html#EC 2.Client.describe_instances --filter-empty By default, missing values are returned as null to keep private/public ip/hostname sets of equal length. This removes null values from the filter
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