Netops with Emacs and Org mode

Org mode is a package for Emacs to “keep notes, maintain todo lists, planning projects and authoring documents”. It can execute embedded snippets of code and capture the output (through Babel). It’s an invaluable tool for documenting your infrastructure and your operations.

Here are three (relatively) short videos exhibiting Org mode use in the context of network operations. In all of them, I am using my own junos-mode which features the following perks:

• syntax highlighting for configuration files,
• commit of configuration snippets to remote devices, and
• execution of remote commands.

Since some Junos devices can be quite slow, commits and remote executions are done asynchronously¹ with the help of a Python helper.

In the first video, I take some notes about configuring BGP add-path feature (RFC 7911). It demonstrates all the available features of junos-mode.

In the second video, I execute a planned operation to enable this feature in production. The document is a modus operandi and contains the configuration to apply and the commands to check if it works as expected. At the end, the document becomes a detailed report of the operation.

In the third video, a cookbook has been prepared to execute Continue reading

Integration of a Go service with systemd

Unlike other programming languages, Go’s runtime doesn’t provide a way to reliably daemonize a service. A system daemon has to supply this functionality. Most distributions ship systemd which would fit the bill. A correct integration with systemd is quite straightforward. There are two interesting aspects: readiness & liveness.

As an example, we will daemonize this service whose goal is to answer requests with nifty 404 errors:

package main

import (
    "log"
    "net"
    "net/http"
)

func main() {
    l, err := net.Listen("tcp", ":8081")
    if err != nil {
        log.Panicf("cannot listen: %s", err)
    }
    http.Serve(l, nil)
}

You can build it with go build 404.go.

Here is the service file, 404.service¹:

[Unit]
Description=404 micro-service

[Service]
Type=notify
ExecStart=/usr/bin/404
WatchdogSec=30s
Restart=on-failure

[Install]
WantedBy=multi-user.target

Readiness

The classic way for an Unix daemon to signal its readiness is to daemonize. Technically, this is done by calling fork(2) twice (which also serves other intents). This is a very common task and the BSD systems, as well as some other C libraries, supply a daemon(3) Continue reading

Write your own terminal emulator

I was an happy user of rxvt-unicode until I got a laptop with an HiDPI display. Switching from a LoDPI to a HiDPI screen and back was a pain: I had to manually adjust the font size on all terminals or restart them.

VTE is a library to build a terminal emulator using the GTK+ toolkit, which handles DPI changes. It is used by many terminal emulators, like GNOME Terminal, evilvte, sakura, termit and ROXTerm. The library is quite straightforward and writing a terminal doesn’t take much time if you don’t need many features.

Let’s see how to write a simple one.

A simple terminal

Let’s start small with a terminal with the default settings. We’ll write that in C. Another supported option is Vala.

#include <vte/vte.h>

int
main(int argc, char *argv[])
{
    GtkWidget *window, *terminal;

    /* Initialise GTK, the window and the terminal */
    gtk_init(&argc, &argv);
    terminal = vte_terminal_new();
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "myterm");

    /* Start a new shell */
    gchar **envp = g_get_environ();
    gchar **command = (gchar * Continue reading