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diff --git a/content/blog/aws/ansible-fact-metadata.md b/content/blog/aws/ansible-fact-metadata.md new file mode 100644 index 0000000..3c48f1c --- /dev/null +++ b/content/blog/aws/ansible-fact-metadata.md @@ -0,0 +1,88 @@ +--- +title: 'Shell script for gathering imdsv2 instance metadata on AWS ec2' +description: 'An ansible fact I wrote' +date: '2024-10-12' +tags: +- ansible +- aws +--- + +## Introduction + +I wrote a shell script to gather ec2 instance metadata with an ansible fact. + +## The script + +I am using POSIX `/bin/sh` because I wanted to support a variety of operating systems. Besides that, the only dependency is `curl`: + +``` shell +#!/bin/sh +set -eu + +metadata() { + local METHOD=$1 + local URI_PATH=$2 + local TOKEN="${3:-}" + local HEADER + if [ -z "${TOKEN}" ]; then + HEADER='X-aws-ec2-metadata-token-ttl-seconds: 21600' # request a 6 hours token + else + HEADER="X-aws-ec2-metadata-token: ${METADATA_TOKEN}" + fi + curl -sSfL --request "${METHOD}" \ + "http://169.254.169.254/latest${URI_PATH}" \ + --header "${HEADER}" +} + +METADATA_TOKEN=$(metadata PUT /api/token) +KEYS=$(metadata GET /meta-data/tags/instance "${METADATA_TOKEN}") +PREFIX='{' +for KEY in $KEYS; do + VALUE=$(metadata GET "/meta-data/tags/instance/${KEY}" "${METADATA_TOKEN}") + printf '%s"%s":"%s"' "${PREFIX}" "${KEY}" "${VALUE}" + PREFIX=',' +done +printf '}' +``` + +## Bonus version without depending on curl + +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: + +``` shell +metadata() { + local METHOD=$1 + local URI_PATH=$2 + local TOKEN="${3:-}" + local HEADER + if [ -z "${TOKEN}" ]; then + HEADER='X-aws-ec2-metadata-token-ttl-seconds: 21600' # request a 6 hours token + else + HEADER="X-aws-ec2-metadata-token: ${METADATA_TOKEN}" + fi + printf "${METHOD} /latest${URI_PATH} HTTP/1.0\r\n%s\r\n\r\n" \ + "${HEADER}" \ + | nc -w 5 169.254.169.254 80 | tail -n 1 +} +``` + +## Deploying an ansible fact + +I deploy the script this way: +``` yaml +- name: 'Deploy ec2 metadata fact gathering script' + copy: + src: 'ec2_metadata.sh' + dest: '/etc/ansible/facts.d/ec2_metadata.fact' + owner: 'root' + mode: '0500' + register: 'ec2_metadata_fact' + +- name: 'reload facts' + setup: 'filter=ansible_local' + when: 'ec2_metadata_fact.changed' +``` + +## Conclusion + +It works, is simple and I like it. I am happy! |