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CloudFormation Userdata

Here’s another way to add startup scripts to your instance during creation.

      UserData:
        Fn::Base64: !Sub |
          #cloud-config
          repo_upgrade: none
 
          runcmd:
            # Cloud init startup script
            - "bash /root/setup.sh"
 
          write_files:
            # Cloud init startup script
            - owner: root:root
              permissions: '0644'
              path: /root/setup.sh
              content: |
                #! /bin/bash -x
          write_files:
            # Cloud init startup script
            - owner: root:root
              permissions: '0644'
              path: /root/setup.sh
              content: |
                #! /bin/bash -x
                # run your bash commands here
                date > log.txt
                uptime >>  log.txt

The above script creates a file setup.sh and executes it during instance creation. The output is dumped to log.txt file.

Create Instance With Alias IP

How to create an instance from a snapshot with alias IP and reserved IPs.

#!/bin/bash
gcloud beta compute instances create jump-server \
--network-interface=aliases=10.128.1.0/24,private-network-ip=jump-server,subnet=default \
--machine-type=n1-standard-1 \``
--network-tier=PREMIUM \
--maintenance-policy=MIGRATE \
--service-account=xxxxxxxxxxxxx-compute@developer.gserviceaccount.com \
--tags=int-webserver \
--image=debian-10-buster-v20201216 \
--image-project=debian-cloud \
--boot-disk-size=20GB \
--boot-disk-type=pd-standard \
--boot-disk-device-name=jump-server-1 \
--no-shielded-secure-boot \
--shielded-vtpm \
--shielded-integrity-monitoring \
--labels=name=jump-server \
--reservation-affinity=any \
--zone=us-central1-a \
--project=airy-totality-151318

The default command uses –private-network-ip and –subnet options separately.

--private-network-ip 10.0.0.24 \
--subnet=default \

But when dealing with aliases, reserved IPs and subnets, use a single –network-interface option instead.

--network-interface=aliases=10.128.1.0/24,private-network-ip=jump-server,subnet=default \

Mounting Duplicate UUIDs

While trying to recover a directory from backup, I ran into an issue with duplicate uuids when trying to mount a recovered volume. The problem was the recovered volume had the same uuid as boot.

Here’s the original mount command I ran, but I was getting a wrong fs type error.

mkdir
mount -t xfs /dev/nvme3n1p2 /recover
mount: wrong fs type, bad option, bad superblock on /dev/nvme3n1p2,
       missing codepage or helper program, or other error

It turned out to be a duplicated uuid. To get around this problem, I ran -o nouuid.

mount -t xfs -o nouuid /dev/nvme3n1p2 /recover

Once the files were recovered, I unmounted volume and detached it from the instance.