Author Archives: James Coyle

Mysql Data Types and Sizes for String/ Text

Category : How-to

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MySQL or MariaDB has several data types for handling text-based characters. There are several data types for handling smaller strings such as CHAR and VARCHAR data types. For larger text-based strings there are BLOB based data types such as TEXT.

It’s worth noting at this point that the below-quoted sizes do not necessarily represent the number of characters they can hold. In addition, more recent versions of MySQL (version 5 and 8) counts characters when defining the length, however, prior to these versions byres were used.

The below table shows the ‘size’ of each data type – notice that some data types are mentioned in characters, and others in bytes. The number of characters are always used when defining a string data type in your DDL statement – for example, VARCHAR(10).

Data TypeSizeDescription
CHAR(n)255 charactersFixed-length character field. Rows are padded with whitespace to the defined length.
VARCHAR(n)65,535 bytes *Variable-length character field with no manipulation on INSERT or SELECT.
TINYTEXT255 bytesVariable-length and stored off-row. Can only be sorted and grouped by up to max_sort_length characters
TEXT(n)65,535 bytes Variable-length and stored off-row. Can only be sorted and grouped by up to max_sort_length characters
MEDIUMTEXT(n)16,777,215 bytes (16MB)Variable-length and stored off-row. Can only be sorted and grouped by up to max_sort_length characters
LONGTEXT(n)4,294,967,295 bytes (4GB)Variable-length and stored off-row. Can only be sorted and grouped by up to max_sort_length characters
ENUM2 bytesThe ENUM doesn’t need a size definition but can hold up to 65,535 values.

* The maximum row length in MySQL is 65,535 bytes – your total row size cannot exceed this byte value. Keep in mind that some character sets consume more than one byte per character. For example, utf8mb4 can take up to 4 bytes per character and therefore the maximum VARCHAR is approximately one-quarter of the maximum row size.

Docker Compose yml for Gitlab and Gitlab Runner

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version: '3.5'
    image: gitlab/gitlab-ce:latest
    restart: unless-stopped
        gitlab_rails['gitlab_shell_ssh_port'] = 8822
      - "8000:80"
      - "8822:22"
      - ./config/gitlab:/etc/gitlab
      - ./data/gitlab:/var/opt/gitlab
      - ./logs:/var/log/gitlab
      - gitlab

    image: gitlab/gitlab-runner:alpine
    restart: unless-stopped
      - gitlab
      - ./config/gitlab-runner:/etc/gitlab-runner
      - /var/run/docker.sock:/var/run/docker.sock
      - gitlab


Create a new directory and save the above file inside it as docker-compose.yml. You’ll need to replace the field hostname with the external URL that you’ll use to access your Gitlab instance.

mkdir gitlab
vi gitlab\docker-compose.yml

Run docker-compose up -d to fetch the images from the docker hub and create your Gitlab instance. You’ll be able to access Gitlab from a browser on port 8000 and the SSH on port 8822.

Dockerfile for Apache Traffic Server (ATS)

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Apache Traffic Server is an enterprise-grade proxy and caching server initially developed by Yahoo, then later made open source and managed by the Apache Foundation.

The below code is a Dockerfile that will download and build ATS on the latest Ubuntu base image. Currently, we’re using Apache Traffic Server version 8.0.5, but if you’d like to use a different version or check for a later version then you’ll need to replace the curl command with one of the downloads available from here.

Create a new folder on your Docker host and add the below text to the dockerfile.

mkdir ats
vi ats/dockerfile
FROM ubuntu:latest
# Update the package repository
RUN set -x \
 && DEBIAN_FRONTEND=noninteractive apt-get update \
 && DEBIAN_FRONTEND=noninteractive apt-get upgrade -y \
 && DEBIAN_FRONTEND=noninteractive apt-get install -y \
        curl \
        locales \
        build-essential \
        bzip2 \
        libssl-dev \
        libxml2 \
        libxml2-dev \
        libpcre3 \
        libpcre3-dev \
        tcl \
        tcl-dev \
        libboost-dev \
    # Configure locale
 && export LANGUAGE=en_US.UTF-8 \
 && export LANG=en_US.UTF-8 \
 && export LC_ALL=en_US.UTF-8 \
 && locale-gen en_US.UTF-8 \
 && DEBIAN_FRONTEND=noninteractive dpkg-reconfigure locales
    # Get ATS and build
RUN  mkdir /tmp/trafficserver \
 && cd /tmp/trafficserver \
 && curl -L | tar -xj --strip-components 1 \
 && ./configure \
 && make install \
 && make distclean \
 && cd / \
    # Clean-up
 && apt-get purge --auto-remove -y \
        curl \
        build-essential \
        bzip2 \
        libssl-dev \
        libxml2-dev \
        libpcre3-dev \
        tcl-dev \
        libboost-dev \
 && apt-get clean \
 && rm -rf /tmp/* /var/lib/apt/lists/*

RUN ln -s /usr/local/etc/trafficserver /etc/trafficserver

ENTRYPOINT ["/usr/local/bin/traffic_server"]

To build the Apache Traffic Server image, cd into the ats directory and issue the build command. The period (.) at the end of the build command is there on purpose – make sure you include it in your build command.

cd ats
docker build -t ats .

The build will take a few minutes, depending on your hardware, but will return you to the command line once completed.

Run your dockerfile and ATS will be available on port 8080, however, you’ll need to configure it as required. The config, such as remap.conf, is contained in /etc/trafficserver

Install Docker-Compose

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Docker-compose is a utility used to create and manage multiple Docker containers together to form a service. It relies on Docker being installed on the same host so make sure that Docker is installed on your system beforehand. Once you have docker installed and tested you’re ready to begin.

It’s worth noting that docker-compose is often available with your Linux distributions package manager, such as apt or yum but you may find they’re often out of date.

Manually installing docker-compose

Manually installing docker-compose is made easy by the fact that the docker-compose binary is a single file. The process is simple; grab the binary, put it in the right place and make it executable.

In addition to Docker, you’ll need curl installed to download the docker-compose binaries.

apt install curl
# Or
yum install curl

Once you have curl installed it’s time to install docker-compose. The below link will install the latest ‘stable’ release – if you need a different release you’ll need to check the github page for the version number you require.

Run the below commands to download docker-compose and link the binary to your linux bin directory.

curl -L "$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
chmod +x /usr/local/bin/docker-compose

Test docker-compose

Finally, to test your docker-compose is working, run the below command to output the version of docker-compose. At the time of writing, the latest version was 1.24.1, but this will move as time goes on.

docker-compose --version
docker-compose version 1.24.1, build 4667896b

How to test your Docker install is working

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Category : How-to

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Testing Docker, thankfully is one of the easiest things you can do – something you’d expect from Docker. With a simple one-liner you can test if your docker instance can reach the central repository, download images and run the image on the local machine.

If you haven’t installed Docker yet, see the installing Docker blog post.

To get started, open a terminal and connect to your docker instance. Once logged in, run the below command.

docker run hello-world

You’ll see some output from Docker detailing what it’s doing. This can be useful to diagnose any problems with your docker instance.

The text that you’re looking for is ‘Hello from Docker!’ – if you see that in the output then your Docker instance is up and running!

The full output will be something similar to the below:

Unable to find image 'hello-world:latest' locally
latest: Pulling from library/hello-world
1b930d010525: Pull complete
Digest: sha256:b8ba256769a0ac28dd126d584e0a2011cd2877f3f76e093a7ae560f2a5301c00
Status: Downloaded newer image for hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:

For more examples and ideas, visit:

Docker Compose yml for WordPress

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The below docker-compose yml file will create two Docker containers for running WordPress; a MySQL database and an Apache PHP web server.

version: '3.6'

        image: mysql:5.7
        container_name: wp_mysql
          - ./data/mysql:/var/lib/mysql
        restart: unless-stopped
            MYSQL_ROOT_PASSWORD: [root password]
            MYSQL_DATABASE: wordpress
            MYSQL_USER: wordpress
            MYSQL_PASSWORD: [wp password]

        image: wordpress:latest
        container_name: wp_web
            - db
            - 8000:80
        restart: unless-stopped
            WORDPRESS_DB_HOST: db:3306
            WORDPRESS_DB_USER: wordpress
            WORDPRESS_DB_NAME: wordpress
            WORDPRESS_DB_PASSWORD: [wp password]
            - ./data/wp_content:/var/www/html/wp-content
            - ./config/wordpress/uploads.ini:/usr/local/etc/php/conf.d/uploads.ini

Create a new directory and save the above file inside it as docker-compose.yml

mkdir wordpress
vi docker-compose.yml

Run docker-compose up -d to fetch the images from the docker hub and create your WordPress instance. You’ll be able to access WordPress from a browser on port 8000.

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