This article mentions that a key piece of software they use in all this is Slony[0], software which allows replicating one primary/master to many secondaries/slaves, even when those replicas have different versions. That's pretty cool, but I'd like to instead draw your attention (dear reader) to the phenomenal writing happening in Slonys description of itself. It describes, in plain but technical language what Slony is, then immediately jumps into addressing "why should you use this?" and does so very directly. It reiterates the problem it solves, mentions other potential solutions by name to contextualize the current solution space, then explains in a nice bulleted list exactly the situations and niches that Slony is tailored for.

Oh my heavens, I wish every piece of technology described itself this way!

[0] - Slony -- https://www.slony.info/