89 lines
2.2 KiB
Markdown
89 lines
2.2 KiB
Markdown
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---
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title: 'Shell script for gathering imdsv2 instance metadata on AWS ec2'
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description: 'An ansible fact I wrote'
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date: '2024-10-12'
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tags:
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- ansible
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- aws
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---
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## Introduction
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I wrote a shell script to gather ec2 instance metadata with an ansible fact.
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## The script
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I am using POSIX `/bin/sh` because I wanted to support a variety of operating systems. Besides that, the only dependency is `curl`:
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``` shell
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#!/bin/sh
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set -eu
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metadata() {
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local METHOD=$1
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local URI_PATH=$2
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local TOKEN="${3:-}"
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local HEADER
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if [ -z "${TOKEN}" ]; then
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HEADER='X-aws-ec2-metadata-token-ttl-seconds: 21600' # request a 6 hours token
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else
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HEADER="X-aws-ec2-metadata-token: ${METADATA_TOKEN}"
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fi
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curl -sSfL --request "${METHOD}" \
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"http://169.254.169.254/latest${URI_PATH}" \
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--header "${HEADER}"
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}
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METADATA_TOKEN=$(metadata PUT /api/token)
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KEYS=$(metadata GET /meta-data/tags/instance "${METADATA_TOKEN}")
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PREFIX='{'
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for KEY in $KEYS; do
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VALUE=$(metadata GET "/meta-data/tags/instance/${KEY}" "${METADATA_TOKEN}")
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printf '%s"%s":"%s"' "${PREFIX}" "${KEY}" "${VALUE}"
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PREFIX=','
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done
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printf '}'
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```
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## Bonus version without depending on curl
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Depending on curl can be avoided. If you are willing to use netcat instead and be declared a madman by your colleagues, you can rewrite the function with:
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``` shell
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metadata() {
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local METHOD=$1
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local URI_PATH=$2
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local TOKEN="${3:-}"
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local HEADER
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if [ -z "${TOKEN}" ]; then
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HEADER='X-aws-ec2-metadata-token-ttl-seconds: 21600' # request a 6 hours token
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else
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HEADER="X-aws-ec2-metadata-token: ${METADATA_TOKEN}"
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fi
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printf "${METHOD} /latest${URI_PATH} HTTP/1.0\r\n%s\r\n\r\n" \
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"${HEADER}" \
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| nc -w 5 169.254.169.254 80 | tail -n 1
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}
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```
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## Deploying an ansible fact
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I deploy the script this way:
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``` yaml
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- name: 'Deploy ec2 metadata fact gathering script'
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copy:
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src: 'ec2_metadata.sh'
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dest: '/etc/ansible/facts.d/ec2_metadata.fact'
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owner: 'root'
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mode: '0500'
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register: 'ec2_metadata_fact'
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- name: 'reload facts'
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setup: 'filter=ansible_local'
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when: 'ec2_metadata_fact.changed'
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```
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## Conclusion
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It works, is simple and I like it. I am happy!
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