Category Archives: Administration

Docker and Kubernetes basics for developers

Docker Docker containers are much more lightweight compared to classic VMs as they leverage host OS instead of starting their own OS. Containers are using 2 features of Linux-based OS: Namespaces and Cgroups (Control Groups). Namespace Lets you allocate resources in an isolated environment (like a sandbox). On a container start, docker daemon generates a …

How to install Outline VPN on a random VPS server

In Ountline Manager, when you add a new server, select an option called «Set up Outline everywhere».

How to reinstall MacOS on M1 MacBook wiping previous admin

I’ve run into an issue when I gave my older MacBook with M1 chip to my wife. Even after reinstalling MacOS with a proper user for her and restoring from Time Machine, her admin account was not really the admin of that laptop. She was unable to create new users (MacOs failed to set a …

DataDog: use events in dashboards

Using events as datasource is pretty straightforward, and described here — https://docs.datadoghq.com/events/. To use it as a graph overlay (for instance, to show app deployments), you can edit your graph, Event Overlays, and add something like below:

tags:tool:morty,dd_env:$env [something like order-history-*]

1	tags:tool:morty,dd_env:$env [something like order-history-*]

Fixing docker does not want to update images

If you run docker pull, and you see an error like failed to register layer: Error processing tar file(exit status 2): fatal error: runtime: out of memory, there could be 2 reasons. Obvious one — not enough disk space for docker. You can fix it with

docker system prune -af
docker volume ls -qf dangling=true

1 2	docker system prune -af docker volume ls -qf dangling=true

WARNING: It will remove your unused resources like …

How to add and increase swap on CentOS

Adding a swap file without reboot If you are having a dedicated server somewhere with not that much memory, you could decide to add a swap without rebooting your server. To do so, you need to follow the routine:

sudo dd if=/dev/zero of=/swapfile count=1024 bs=1MiB
sudo mkswap /swapfile
sudo chmod 0600 /swapfile
sudo swapon /swapfile

sudo dd if=/dev/zero of=/swapfile count=1024 bs=1MiB

sudo mkswap /swapfile

sudo chmod 0600 /swapfile

sudo swapon /swapfile

Increasing a swap size If something goes wrong with your system, and you see that …

How to install multiple versions of go on mac m1

For instance, I want to try a new beta, go1.18beta2 (I check if it’s available on the download page). And I already have a regular go1.17, that I want to use as a default one. To do so, I need to do this:

go install golang.org/dl/go1.18beta2@latest
go1.18beta2 download

1 2	go install golang.org/dl/go1.18beta2@latest go1.18beta2 download

Then I can check if it’s okay — go1.18beta2 version #go …

Create SQS queues on localstack container start

Put this file to your filesystem as ←anyname.sh→:

#!/usr/bin/env bash

set -euo pipefail

# enable debug
# set -x


echo "configuring sqs"
echo "==================="
LOCALSTACK_HOST=localhost
AWS_REGION=eu-central-1


# https://docs.aws.amazon.com/cli/latest/reference/sqs/create-queue.html
create_queue() {
	local QUEUE_NAME_TO_CREATE=$1
	awslocal --endpoint-url=http://${LOCALSTACK_HOST}:4566 sqs create-queue --queue-name ${QUEUE_NAME_TO_CREATE} --region ${AWS_REGION} --attributes VisibilityTimeout=30
}

create_queue "queue2"
create_queue "queue1"

#!/usr/bin/env bash

set -euo pipefail

# enable debug

# set -x

echo "configuring sqs"

echo "==================="

LOCALSTACK_HOST=localhost

AWS_REGION=eu-central-1

# https://docs.aws.amazon.com/cli/latest/reference/sqs/create-queue.html

create_queue() {

local QUEUE_NAME_TO_CREATE=$1

awslocal --endpoint-url=http://${LOCALSTACK_HOST}:4566 sqs create-queue --queue-name ${QUEUE_NAME_TO_CREATE} --region ${AWS_REGION} --attributes VisibilityTimeout=30

}

create_queue "queue2"

create_queue "queue1"

For instance, ./localstack_bootstrap/sqs_bootstrap.sh. Don’t forget to run chmod +x ./localstack_bootstrap/sqs_bootstrap.sh. Add this line to your docker-compose.yml: — ./localstack_bootstrap:/docker-entrypoint-initaws.d/. So it could look like this:

services:
  localstack:
    container_name: aws_sqs
    hostname: sqs
    image: localstack/localstack:latest
    environment:
      - AWS_DEFAULT_REGION=ap-southeast-1
      - EDGE_PORT=4566
      - SERVICES=sqs
    ports:
      - '4566:4566'
    volumes:
      - "${TMPDIR:-/tmp/localstack}:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"
      - ./localstack_bootstrap:/docker-entrypoint-initaws.d/

services:

localstack:

container_name: aws_sqs

hostname: sqs

image: localstack/localstack:latest

environment:

- AWS_DEFAULT_REGION=ap-southeast-1

- EDGE_PORT=4566

- SERVICES=sqs

ports:

- '4566:4566'

volumes:

- "${TMPDIR:-/tmp/localstack}:/tmp/localstack"

- "/var/run/docker.sock:/var/run/docker.sock"

- ./localstack_bootstrap:/docker-entrypoint-initaws.d/

Then your queues can be reached by URLs http://localhost:4566/000000000000/queue1 and http://localhost:4566/000000000000/queue2. Further reading: https://docs.aws.amazon.com/cli/latest/reference/sqs/create-queue.html https://joerg-pfruender.github.io/software/docker/microservices/testing/2020/01/25/Localstack_in_Docker.html

Parental control for Linux Mint

Time limiter with UI — Timekpr (https://www.linuxuprising.com/2019/11/timekpr-next-is-linux-parental-control.html) Domain blocker — Mintnanny (https://www.reallinuxuser.com/how-to-setup-parental-control-in-linux-mint/), too simple.

Shell: repeat a task multiple time

All shells (bash/zsh):

watch -n 3 "curl --location --request GET 'http://...'"

1	watch -n 3 "curl --location --request GET 'http://...'"

will run curl every 3 seconds until you break it. zsh specific:

repeat 5 { curl --location --request GET 'http://...' }

1	repeat 5 { curl --location --request GET 'http://...' }

will repeat it 5 times without any delay