aboutsummaryrefslogtreecommitdiff
path: root/content/blog
diff options
context:
space:
mode:
authorJulien Dessaux2024-10-12 15:28:40 +0200
committerJulien Dessaux2024-10-12 15:28:40 +0200
commit4e29d73c402cee99abd40f91fc2913e6c802a125 (patch)
tree1eaf25a7d7b059b66d6f6cbca8914bb9a8b37bcb /content/blog
parentfixed borg ansible role blog article (diff)
downloadwww-4e29d73c402cee99abd40f91fc2913e6c802a125.tar.gz
www-4e29d73c402cee99abd40f91fc2913e6c802a125.tar.bz2
www-4e29d73c402cee99abd40f91fc2913e6c802a125.zip
add ansible metadata fact on ec2 blog article
Diffstat (limited to '')
-rw-r--r--content/blog/aws/ansible-fact-metadata.md88
1 files changed, 88 insertions, 0 deletions
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!