add ansible metadata fact on ec2 blog article

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!