nixpkgs/nixos/modules/virtualisation/ec2-metadata-fetcher.nix
Jack Kelly 43bfd7e5b1 {ec2,openstack}-metadata-fetcher: unconditionally fetch metadata
The metadata fetcher scripts run each time an instance starts, and it
is not safe to assume that responses from the instance metadata
service (IMDS) will be as they were on first boot.

Example: an EC2 instance can have its user data changed while
the instance is stopped. When the instance is restarted, we want to
see the new user data applied.
2020-11-22 11:04:46 +10:00

78 lines
2.6 KiB
Nix

{ curl, targetRoot, wgetExtraOptions }:
# Note: be very cautious about dependencies, each dependency grows
# the closure of the initrd. Ideally we would not even require curl,
# but there is no reasonable way to send an HTTP PUT request without
# it. Note: do not be fooled: the wget referenced in this script
# is busybox's wget, not the fully featured one with --method support.
#
# Make sure that every package you depend on here is already listed as
# a channel blocker for both the full-sized and small channels.
# Otherwise, we risk breaking user deploys in released channels.
#
# Also note: OpenStack's metadata service for its instances aims to be
# compatible with the EC2 IMDS. Where possible, try to keep the set of
# fetched metadata in sync with ./openstack-metadata-fetcher.nix .
''
metaDir=${targetRoot}etc/ec2-metadata
mkdir -m 0755 -p "$metaDir"
rm -f "$metaDir/*"
get_imds_token() {
# retry-delay of 1 selected to give the system a second to get going,
# but not add a lot to the bootup time
${curl}/bin/curl \
-v \
--retry 3 \
--retry-delay 1 \
--fail \
-X PUT \
--connect-timeout 1 \
-H "X-aws-ec2-metadata-token-ttl-seconds: 600" \
http://169.254.169.254/latest/api/token
}
preflight_imds_token() {
# retry-delay of 1 selected to give the system a second to get going,
# but not add a lot to the bootup time
${curl}/bin/curl \
-v \
--retry 3 \
--retry-delay 1 \
--fail \
--connect-timeout 1 \
-H "X-aws-ec2-metadata-token: $IMDS_TOKEN" \
http://169.254.169.254/1.0/meta-data/instance-id
}
try=1
while [ $try -le 3 ]; do
echo "(attempt $try/3) getting an EC2 instance metadata service v2 token..."
IMDS_TOKEN=$(get_imds_token) && break
try=$((try + 1))
sleep 1
done
if [ "x$IMDS_TOKEN" == "x" ]; then
echo "failed to fetch an IMDS2v token."
fi
try=1
while [ $try -le 10 ]; do
echo "(attempt $try/10) validating the EC2 instance metadata service v2 token..."
preflight_imds_token && break
try=$((try + 1))
sleep 1
done
echo "getting EC2 instance metadata..."
wget_imds() {
wget ${wgetExtraOptions} --header "X-aws-ec2-metadata-token: $IMDS_TOKEN" "$@";
}
wget_imds -O "$metaDir/ami-manifest-path" http://169.254.169.254/1.0/meta-data/ami-manifest-path
wget_imds -O "$metaDir/user-data" http://169.254.169.254/1.0/user-data && chmod 600 "$metaDir/user-data"
wget_imds -O "$metaDir/hostname" http://169.254.169.254/1.0/meta-data/hostname
wget_imds -O "$metaDir/public-keys-0-openssh-key" http://169.254.169.254/1.0/meta-data/public-keys/0/openssh-key
''