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nixpkgs/nixos/modules/virtualisation/ec2-metadata-fetcher.nix

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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 "$metaDir/ami-manifest-path" http://169.254.169.254/1.0/meta-data/ami-manifest-path
(umask 077 && wget_imds -O "$metaDir/user-data" http://169.254.169.254/1.0/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
''