Simple Made Easy (link)

An oldie-but-good I was reminded of recently:

https://www.infoq.com/presentations/Simple-Made-Easy

Rich Hickey emphasizes simplicity’s virtues over easiness’, showing that while many choose easiness they may end up with complexity, and the better way is to choose easiness along the simplicity path.

Sample takeaways:

  • We should aim for simplicity because simplicity is a prerequisite for reliability.
  • Simple is often erroneously mistaken for easy. “Easy” means “to be at hand”, “to be approachable”. “Simple” is the opposite of “complex” which means “being intertwined”, “being tied together”. Simple != easy.

Choose simple constructs over complexity-generating constructs; It's the artifacts, not the authoring; Create abstractions with simplicity as a basis; Simplify the problem space before you start; Simplicity often means making more things, not fewer; Reap the benefits!

He even predicts (to some extent) microservice architecture by declaring a set of separate strings hanging down independently can show a byproduct of simplicity can be more things, but things that are easier to understand and manage than if the strings were intertwined — and easier to update individually.

Swap column values in MySql (via temp variables)

If you want to swap values in one query in MySql without a temporary table, you can use variables to hold values that otherwise would be changed before you can use them.

E.g., swap start_date and end_date via:

UPDATE mydates SET start_date=@tmp:=start_date, start_date=end_date, end_date=@tmp WHERE start_date > end_date

Install amqp-ext PHP extension to Apache in Docker

I wanted to add RabbitMQ support to my PHP app and prefer to use the PECL amqp package:

This extension can communicate with any AMQP spec 0-9-1 compatible server, such as RabbitMQ, OpenAMQP and Qpid, giving you the ability to create and delete exchanges and queues, as well as publish to any exchange and consume from any queue.

Using pecl install won’t install all the dependencies. There are various options to how to solve this including fetching from Git repos, however this is the one that worked for me and seemed the most straight-forward (ymmv). See below for code used in a Dockerfile with base image FROM php:7.1.14-apache which uses debian:jessie, so the native commands should work in similar Debian/Ubuntu linux distros.

RUN curl http://in.archive.ubuntu.com/ubuntu/ubuntu/pool/universe/libr/librabbitmq/librabbitmq4_0.8.0-1_amd64.deb -o librabbitmq4_0.8.0-1_amd64.deb
RUN curl http://in.archive.ubuntu.com/ubuntu/ubuntu/pool/universe/libr/librabbitmq/librabbitmq-dev_0.8.0-1_amd64.deb -o librabbitmq-dev_0.8.0-1_amd64.deb
RUN dpkg -i librabbitmq4_0.8.0-1_amd64.deb
RUN dpkg -i librabbitmq-dev_0.8.0-1_amd64.deb
RUN pecl install amqp-1.9.3 && docker-php-ext-enable amqp

Note if you do use this in a Dockerfile, you can combine some of the statements to optimize layers. You also may need to update the lib version if it’s updated or if you change the PECL version to install.

Docker: get hash from image name

Particularly if you are using a static image name like “latest” or “develop”, it is useful to be able to know and verify the exact version via the sha256 hash. To get the value you can use:

docker inspect --format='{{index .RepoDigests 0}}' repo/image-name:tag

To use this in a CI/CD workflow for Docker Swarm, you can do something like this:

SHA=$(docker inspect --format='{{index .RepoDigests 0}}' repo/image-name:tag)
docker service update --image $SHA --detach=true --with-registry-auth service-name

Remove Docker images with no tag

Sometimes, particularly on a development environment, you can end up with a lot of Docker images with no tags, which aren’t much practical use. To get rid of them you can do:

docker rmi $(docker images | grep none | awk '{ print $3 }')

Ones in use or with child images will not be deleted and result in output warning, but the rest will be removed so you can deal with the remaining ones as needed.

Docker for Mac clock drift fix

It’s a pain, not sure if there is a “real” fix, but if your Docker host and Mac host clocks drift (presumably the Mac is correct), you can run:

docker run --privileged --rm alpine date -s "$(date -u "+%Y-%m-%d %H:%M:%S")"

I’ve seen differences over 5 minutes, so worth checking…

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