Is it Dragonflight, part of the Dragon Riders of Pern series by Anne McCaffrey?
Plot summary of the world and books:
Life on Pern as presented in the novels resembles a pre-industrial society with lords, holds, harpers (musicians, entertainers, and teachers), and dragons, with the occasional examples of higher technology (like flamethrowers, telegraphs, chemical fertilizers, and powerful microscopes and telescopes).
Pernese people are described as belonging to four basic groups: Weyrfolk (including Dragonriders) who live in the Weyrs, the Holders who live in the Holds (cities, towns and farms), the crafters who live in Crafthalls (or are assigned to work their crafts in certain Holds), and the Holdless who have no permanent home (including traders, displaced Holders, and brigands).
One of the main threats to Pernese civilization in the series is Thread, which is described as a mycorrhizoid spore that periodically rains down on the planet due to the orbit of the Red Star. The Red Star is set out to be a rogue planet in the Rukbat system. The Red Star, characterized as a "Sedna-class inner Oort cloud object", has a 250 Turn (or Pernese year) elliptic orbit around its sun. Thread can reach the planet Pern for about 50 Turns while the Red Star is at perihelion. Thread is described in this series as an agent that consumes organic material at a voracious rate, including crops, animals, and any humans in its path.
The Pernese use intelligent firebreathing dragons and their riders to fight Thread. The riders have a telepathic bond with their dragons, formed by Impression at the dragon's hatching. Later books deal with the initial colonization of Pern and the creation of the dragons through genetic manipulation. The lengthy time period covered by the series as a whole (over two and a half millennia) allows room for new stories and characters, explored by each new novel released by the authors.