Information Technology – Page 9

2019-04-302021-09-26

Software Architecture

I’ve performed many roles in my career, but software architecture is what I like most, and I’m pretty good at it.

My recipe for architecting a solution is this. First I study the current processes: I often need to feel the pain of working with them daily. So I work, learn, and discover improvable areas. Then I envision a new architecture that organically fits every piece together, allows simpler processes, and reuses as many building blocks as possible. Then I design a migration path, a chain of reachable steps to perform one at a time, without disrupting production.

Software architectures don’t last long without alterations, not even the best ones, because companies grow along many dimensions. It’s only a matter of time for those changes to go beyond what the architect foresaw. And technical debt ensues.

Software engineers and companies alike need to understand that embracing change (agile anyone?) includes architecting and re-architecting as often as needed.

2018-06-112021-09-26

How to add a link from a featured image to any URL

I want to provide a link to the source of a featured image, that I use to draw attention to a post of mine, to help catalog that as a “fair use”.

Unfortunately, the standard Twentyseventeen theme of WordPress doesn’t offer any way of doing such a simple thing out of the box.

But with the help of my Custom Stuff plugin

<?php
/*
Plugin Name: Custom Stuff
Plugin URI: http://andowebsit.es/
Description: Custom stuff for my blog.
Author: Andrea Ercolino
Author URI: http://andowebsit.es/about
Version: 1.1
*/

function custom_stuff_header() {
    require 'header.php';
}
add_action( 'wp_head',  'custom_stuff_header', 10, 0 );


function custom_stuff_footer() {
    require 'footer.php';
}
add_action( 'wp_footer',  'custom_stuff_footer', 10, 0 );

require 'no-richedit.php';

(file wordpress/wp-content/plugins/custom-stuff/custom-stuff.php)

that’s only a few lines away

<?php

function custom_stuff_featured_image_link($html, $post_id, $post_thumbnail_id) {
    $post_thumbnail = get_post( $post_thumbnail_id );
    if ( ! $post_thumbnail ) {
        return $html;
    }
    $href = $post_thumbnail->post_title;
    if ( ! $href ) {
        return $html;
    }
    return "<a href='$href' target='_blank'>$html</a>";
}

add_filter( 'post_thumbnail_html', 'custom_stuff_featured_image_link', 10, 3 );

(file wordpress/wp-content/plugins/custom-stuff/featured-image-link.php)

<?php
/*
Plugin Name: Custom Stuff
Plugin URI: http://andowebsit.es/
Description: Custom stuff for my blog.
Author: Andrea Ercolino
Author URI: http://andowebsit.es/about
Version: 1.2
*/

function custom_stuff_header() {
    require 'header.php';
}
add_action( 'wp_head',  'custom_stuff_header', 10, 0 );


function custom_stuff_footer() {
    require 'footer.php';
}
add_action( 'wp_footer',  'custom_stuff_footer', 10, 0 );

require 'no-richedit.php';

require 'featured-image-link.php';

(file wordpress/wp-content/plugins/custom-stuff/custom-stuff.php)

2018-06-062021-09-26

How to connect from SequelPro to an Ubuntu server using Public Key authentication

Connecting from SequelPro to an Ubuntu server using Public Key authentication looks like a very simple setup, and in fact it entails just a few steps, but I had to learn again each of them the hard way. After many months without using SequelPro to access my WordPress database on DigitalOcean, my Ubuntu server was already the second new instance since the last time I had configured SequelPro and I hadn’t the slightest idea of which was the last working configuration and how it was set up.

Machines

Remote: the machine you want to connect to with SSH
Local: the machine you want to connect from with SSH

Setup

Remote: Create a group of users with permission to login with SSH
- Open a terminal window on Local and SSH into Remote using the root user
- Run # addgroup sshlogin
- Run # adduser root sshlogin
- Edit the /etc/ssh/sshd_config file and append a line with AllowGroups sshlogin.
- Run # systemctl restart ssh
- Before closing this terminal window, open a new one and try to login with SSH using the root user. If you are denied access, go back to the previous terminal window and try to figure out how to fix root access while you still have root access.
Remote: Create a SequelPro user and add it to the sshlogin group
- Run # adduser sequel_pro
- Run # adduser sequel_pro sshlogin
The SequelPro user is a common user, with its own home directory.

Set a long password, only used to prevent unauthorised impersonation (without an authorised key).
Local: Generate a key pair
- Run $ ssh-keygen -b 4096
I used an empty passphrase to protect the private key.
Remote: Authorise the key for the SequelPro user
- Edit the /home/sequel_pro/.ssh/authorized_keys file and append a line with the pubic key (one long line).
- Run # chown -R sequel_pro:sequel_pro /home/sequel_pro/.ssh
- Run # chmod 0700 /home/sequel_pro/.ssh
- Run # chmod 0600 /home/sequel_pro/.ssh/authorized_keys

Test

(add the SequelPro user to the sshlogin group and) confirm that you can login

andrea at Lock-and-Stock in ~
$ ssh sequel_pro@159.89.188.53
sequel_pro@159.89.188.53: Permission denied (publickey).

andrea at Lock-and-Stock in ~
$ ssh -i ./.ssh/sequel_pro-id_rsa sequel_pro@159.89.188.53
Welcome to Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-127-generic x86_64)
...
sequel_pro@wordpress-1vcpu-2gb-nyc3-01:~$

remove the SequelPro user from the sshlogin group and confirm that you cannot login

root@wordpress-1vcpu-2gb-nyc3-01:/etc/ssh# deluser sequel_pro sshlogin
Removing user `sequel_pro' from group `sshlogin' ...
Done.

andrea at Lock-and-Stock in ~
$ ssh -i .ssh/sequel_pro-id_rsa sequel_pro@159.89.188.53
sequel_pro@159.89.188.53: Permission denied (publickey).

Troubleshooting

On remote
1. Check owner and permissions of the .ssh directory and its contents.
2. Make sure that AllowGroups sshlogin is working nicely with Match rules.
  
  In my case, the former was not working for sequel_pro (i.e. sequel_pro could login both when it belonged to sshlogin and when it did not) because the former appeared just before.