CodeIgniter Base URL

I have a CodeIgniter dev site in Google Cloud. The instance obtains a new IP address at every start. You can set the base URL to a domain or IP address in the “/application/config/config.php” file. Since it’s only a dev box, I don’t have a domain assigned. It’s accessible via IP address only which changes every time the instance is started. So here’s the workaround. I added some extra code in the config file to obtain the external IP address.

$realIP = file_get_contents("");
$config['base_url'] = 'http://'.$realIP;

The code is using a service from which returns your external IP address. Works like a charm!

Nitro-based Instance Volumes

AWS introduced Nitro-based instances which are modular. They are meant for high performance, high availability, and high security systems. Nitro building blocks provide direct access to high-speed local storage over a PCI interface and transparently encrypts all data using dedicated hardware. It also provides hardware-level isolation between storage devices and EC2 instances so that bare metal instances can benefit from local NVMe storage. The following are Nitro-based instances: A1, C5, C5d, C5n, I3en, M5, M5a, M5ad, M5d, p3dn.24xlarge, R5, R5a, R5ad, R5d, T3, T3a, and z1d. Bare metal: c5.metal, c5n.metal, i3.metal, i3en.metal, m5.metal, m5d.metal, r5.metal, r5d.metal, u-6tb1.metal, u-9tb1.metal, u-12tb1.metal, and z1d.metal.

Although Nitro-based instances looks like regular volumes (/dev/xvda) from the AWS Console, inside the operating system, they look (/dev/nvme6n1) completely different.

In AWS Console, the storage devices will look like this.


In the operating system, invoking df -h, results in this.

/dev/nvme0n1p2   30G  7.0G   24G  24% /
/dev/nvme4n1     50G   20G   31G  40% /vol1
/dev/nvme1n1     10G  753M  9.3G   8% /vol2
/dev/nvme8n1    500G   67G  433G  14% /backups
/dev/nvme2n1    400G   12G  388G   3% /vol3
/dev/nvme6n1    150G  150G  755M 100% /vol4
/dev/nvme7n1     10G   33M   10G   1% /vol5
/dev/nvme5n1     10G  553M  9.5G   6% /vol6
/dev/nvme9n1    100G   91G   10G  91% /vol7

The big question is, how can you tell which volume is associated with which. You’ll need nvme program to map out the volumes. Install nvme-cli first.

yum install nvme-cli

Then run the command below.

# run nvme
sudo nvme id-ctrl -v /dev/nvme6n1 | grep xv
# the result
0000: 2f 64 65 76 2f 73 64 6a 20 20 20 20 20 20 20 20 "/dev/xvdf..."

GCP Create Instance From Snapshot

There are two steps in creating an instance from a snapshot.

  1. Create a disk from snapshot
  2. Create an instance from the disk

Create a disk from snapshot.

gcloud compute disks create "hostname-boot" \
--project "project-id" \
--zone "us-central1-a" \
--source-snapshot "snapshot-name" \
--type "pd-standard" \
--size "100"

Create an instance from disk.

gcloud beta compute instances create hostname \
--project=project-id \
--zone=us-central1-a \
--subnet=your-subnetwork \
--machine-type=n1-standard-1 \
--no-address \
--maintenance-policy=MIGRATE \ \
--disk=name=instance-1,device-name=instance-1,mode=rw,boot=yes,auto-delete=yes \
--reservation-affinity=any \
--labels=builtby=john.doe \
--tags=web \
--scopes= \

Force Umount if Busy

If device is busy and you can’t umount it, try it with -l option (lazy unmount). Or you can force it.

# standard
umount /mnt/data
# lazy umount
umount -l /mnt/data
# force
umount -f /mnt/data

Lazy unmount is safer since it will detach immediately and clean up all references to the file system. Force is a bit more drastic.