In my last article I’ve outlined how Kubernetes is overused in some scenarios where it does not suit. I’ve even given some good alternatives. One of the obvious alternatives is deploying containers in Virtual Machines or Managed Instance Groups (MIGs). Let’s explore how we can achieve it with minimal effort.
You can access the commands used in the article via this repository.
Deploying Containers to Virtual Machines
Deploying container images to the VM is pretty straight forward. You just need to be ready with your image and run single command, and rest of the things taken care by GCP for you.
Create VM with container image
Following is the command you can use to create Virtual Machine with container image.
gcloud compute instances create-with-container busybox-vm \
--container-image docker.io/busybox:1.27 \
--container-restart-policy on-failure \
--container-privilegedUpdate VM Containers
You can also update the commands for the container running inside VM.
gcloud compute instances update-container busybox-amv \
--container-command "/bin/ash" --container-arg="-c" \
--container-arg="ls -l"STDIN and TTY in VM Containers
You can allocate a buffer for STDIN in the container runtime to keep the STDIN stream open in a container. If this is not set, reads from STDIN in the container always result in EOF. Also, you can debug by establishing an interactive shell by enabling pseudo-TTY.
gcloud compute instances update-container busybox-vm \
--container-tty \
--container-stdinSupply Environment Variables in VM Containers
You can provide environment variables for your container.
gcloud compute instances create-with-container busybox-vm \
--container-image docker.io/busybox:1.27 \
--container-env HOME=/home,MODE=test,OWNER=adminOr, you can also provide environment variables using env variable file.
gcloud compute instances create-with-container busybox-vm \
--container-image docker.io/busybox:1.27 \
--container-env-file ./env.txtThe file contents look like the following:
# This is an env.text file content
HOME=/home
MODE=test
OWNER=adminYou can remove the environment variables:
gcloud compute instances update-container busybox-vm \
--remove-container-env MODE,OWNERMounting Volumes in VM Containers
Mouning a host directory as a data volume:
gcloud compute instances create-with-container busybox-vm \
--container-image docker.io/busybox:1.27 \
--container-mount-host-path mount-path=/logs,host-path=/tmp,mode=rwRemoving volume mounts
gcloud compute instances update-container busybox-vm \
--remove-container-mounts /logsMounting tempfs file system as a data volume
gcloud compute instances create-with-container busybox-vm \
--container-image docker.io/busybox:1.27 \
--container-mount-tmpfs mount-path=/cacheRemoving tempfs volume
gcloud compute instances update-container busybox-vm \
--remove-container-mounts /cacheMounting Persistent Disks
Creating and mounting persistent disks
gcloud compute instances create-with-container busybox-vm \
--disk name=my-data-disk \
--create-disk name=my-scratch-disk,auto-delete=yes,image=ubuntu-1710-artful-v20180315,image-project=ubuntu-os-cloud \
--container-image docker.io/busybox:1.27 \
--container-mount-disk mount-path="/disks/data-disk",name=my-data-disk,mode=ro \
--container-mount-disk mount-path="/disks/scratch-disk",name=my-scratch-diskRemoving/Updating mounts
gcloud compute instances update-container busybox-vm \
--container-mount-disk mount-path="/disks/data-disk",name=my-data-disk,mode=rw \
--remove-container-mounts "/disks/scratch-disk"Allow traffic to VM Containers
VMs with containers use the host network mode, where a container shares the host’s network stack and all interfaces from the host are available to the container.
Container ports have a one-to-one mapping to the host VM ports. For example, a container port 80 maps to the host VM port 80. Compute Engine does not support the port publishing (-p) flag, and you do not have to specify it for the mapping to work.
To publish a container’s ports, configure firewall rules to enable access to the host VM instance’s ports. The corresponding ports of the container are accessible automatically, according to the firewall rules.
Step 1: Create VM with NGINX container
gcloud compute instances create-with-container nginx-vm \
--container-image gcr.io/cloud-marketplace/google/nginx1:1.15 \
--tags http-serverThe container shares the host VM’s network stack, and the container’s port 80 is published to the host VM’s port 80. The http-server tag is used as a target tag for the firewall rule
Step 2: Create a firewall rule to enable connections to port 80 of the VM instance
gcloud compute firewall-rules create allow-http \
--allow tcp:80 \
--target-tags http-serverThe container automatically starts receiving traffic on port 80.
Debug VM Containers
You can also ssh VM containers and debug the issue you are facing in your containers.
gcloud beta compute ssh nginx-vm \
--zone=us-central1-a \
--container={CONTAINER-ID OR CONTAINER-NAME}
Deploying Containers on an MIG (Managed Instance Group)
There are two major steps involved in creating MIGs with container images.
Step 1: Create an instance template
gcloud compute instance-templates create-with-container nginx-instance-template \
--container-image=gcr.io/cloud-marketplace/google/nginx:1.20 \
--container-restart-policy on-failure \
--container-privilegedStep 2: Create an MIG with the Instance Template
gcloud compute instance-groups managed create nginx-group \
--base-instance-name nginx-vm \
--size 2 \
--template nginx-instance-templateSSH your container image
gcloud beta compute ssh nginx-vm-{####} \
--container nginx-instance-templateCreate Autoscaling and Multi-zone MIG
Create MIG in multi-zone
gcloud compute instance-groups managed create nginx-group \
--base-instance-name nginx-vm \
--size 8 \
--template nginx-instance-template \
--zones us-east1-b,us-east1-c
Set autoscaling
gcloud compute instance-groups managed set-autoscaling nginx-group \
--max-num-replicas 20 \
--target-cpu-utilization 0.60 \
--cool-down-period 90Challenge
I left with the challenge here. There is a way to create stateful MIGs with persistent disks. You need to create instance template with container image mounting persistent disks and then create stateful MIG (with persistent disk) with the instance template. You can put your answer as a comment.
Conclusion
So, ideally you have options to Kubernetes when it’s absolutely not required like I mentioned in my last article.