cloud-init hostnames

cloud-init_prefix_hostname.sh

#!/bin/bash

# /var/lib/cloud/scripts/per-boot/00-hostname.sh

# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#scripts-per-boot

#
# create/set server hostname using a static prefix with a cloud instance id appended.
#
# sed -i '' \
#  's/instance_name_prefix="NOT-CONFIGURED"/instance_name_prefix="cloudserver"/g' \
#   /var/lib/cloud/scripts/per-boot/00-hostname.sh
# 
# would result in something like: 
#   cloudserver-ac283a2e52
#

 
instance_name_prefix="NOT-CONFIGURED"

# if our script hasnt been configured, exit
if [ ${instance_name_prefix} == "NOT-CONFIGURED" ]; then
    exit 0
fi
 
# generate a token for the metadata service
TOKEN="$(curl --silent -X PUT """http://169.254.169.254/latest/api/token""" -H """X-aws-ec2-metadata-token-ttl-seconds: 300""")"

# take our instance id and strip the "i-" from the front
instance_id="$(curl --silent -H """X-aws-ec2-metadata-token: ${TOKEN}""" http://169.254.169.254/latest/meta-data/instance-id)"
instance_id="${instance_id##*-}"
 
# then append the id to our hostname prefix
new_hostname="${instance_name_prefix}-${instance_id}"
 
# and update our hostname
hostnamectl set-hostname "${new_hostname}"
hostnamectl set-hostname --static "${new_hostname}"
hostnamectl

cloud-init_prefix_hostname2.sh

#!/bin/bash

# /var/lib/cloud/scripts/per-boot/00-hostname.sh

# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#scripts-per-boot

#
# create/set server hostname using a static prefix with a cloud instance id appended.
#
# sed -i '' \
#  's/instance_name_prefix="NOT-CONFIGURED"/instance_name_prefix="cloudserver"/g' \
#   /var/lib/cloud/scripts/per-boot/00-hostname.sh
# 
# would result in something like: 
#   cloudserver-ac283a2e52
#

instance_name_prefix="NOT-CONFIGURED"

# if our script hasnt been configured, exit
if [ ${instance_name_prefix} == "NOT-CONFIGURED" ]; then
    exit 0
fi
 
# if our script hasnt been configured, exit
if [ ${instance_name_prefix} == "NOT-CONFIGURED" ]; then
    exit 0
fi

AWS_URL="http://169.254.169.254/latest/meta-data/instance-id"
AWS_TOKEN_URL="http://169.254.169.254/latest/api/token"
GCP_URL="http://169.254.169.254/computeMetadata/v1/instance/id"


if AWS_TOKEN="$(curl --silent -X PUT ${AWS_TOKEN_URL} -H """X-aws-ec2-metadata-token-ttl-seconds: 300""")"; then
        # we're running in AWS
        # retrive our identity document
        _instance_id="$(curl --silent -H """X-aws-ec2-metadata-token: ${AWS_TOKEN}""" ${AWS_URL})"
        # generate our new hostname
        new_hostname="${instance_name_prefix}-${_instance_id##*-}"
        :;
elif curl --silent --output /dev/null --fail --connect-timeout 10 ${GCP_URL} --header "Metadata-Flavor: Google"; then
        # we're running in GCP
        # get our instance id
        _instanceid="$(curl --silent -H 'Metadata-Flavor: Google' ${GCP_URL})"
        # generate our new hostname
        new_hostname="${instance_name_prefix}-${_instanceid/i-/}"
        :;
else
        # we're not in cloud
        new_hostname="${instance_name_prefix}"
        :;
fi

hostnamectl set-hostname "${new_hostname}"
hostnamectl set-hostname --static "${new_hostname}"
hostnamectl

cloud-init_tag_hostname.sh

#!/bin/bash

# /var/lib/cloud/scripts/per-boot/00-hostname.sh

# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#scripts-per-boot
 
#
# create/set server hostname using the "Name" tag/label and 
# append the cloud instance id
#
# eg: <name tag/label>-<instance_id>
#

AWS_URL="http://169.254.169.254/latest/meta-data/"
GCP_URL="http://169.254.169.254/computeMetadata/v1/instance/"
 
if curl --silent --output /dev/null --fail --connect-timeout 10 ${AWS_URL}; then
        # we're running in AWS
         
        # retrive our identity document
        _identity_document=$(curl -s http://169.254.169.254/latest/dynamic/instance-identity/document)
         
        # get region from identity doc
        _region=$(jq -r .region <<< "${_identity_document}")
         
        # get instance_id from identity doc
        _instanceid="$(jq -r .instanceId <<< "${_identity_document}")"
         
        # get the value of the "Name" tag
        _tags=$(aws ec2 describe-tags  --filter "Name=resource-id,Values=${_instanceid}" --region "${_region}")
        _tag_name=$(jq -r '.Tags[] | select(.Key=="Name") | .Value' <<< "${_tags}")
 
        # construct a "nice, unique hostname" using the value of name tag and instance id
        new_hostname="${_tag_name}-${_instanceid/i-/}"
 
 
elif curl --silent --output /dev/null --fail --connect-timeout 10 ${GCP_URL} --header "Metadata-Flavor: Google"; then
        # we're running in GCP
         
        # get our instance id
        _instanceid=$(curl -s -H 'Metadata-Flavor: Google'  http://metadata.google.internal/computeMetadata/v1/instance/id)
         
        # get our instance name (from tag)
        _name=$(curl -s -H 'Metadata-Flavor: Google'  http://metadata.google.internal/computeMetadata/v1/instance/name)
        
        # construct a "nice, unique hostname" using the value of name label and instance id
        new_hostname="${_name}-${_instanceid/i-/}"
        :;
else
        # we're not in cloud
        exit 0
        :;
fi
 
 
hostnamectl set-hostname "${new_hostname}"
hostnamectl set-hostname --static "${new_hostname}"
hostnamectl
EOF

preserve_hostname.cfg

# prevent cloud-init from resetting your instance name

# For those times when you absolutely, positively need to run your datacentre in the cloud!

# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#set-hostname
# https://cloudinit.readthedocs.io/en/latest/topics/modules.html#update-hostname

preserve_hostname: true