That book is a classic overview by a very knowledgeable person ( Cal
Henderson co-founded Flickr and now Slack). I'm sure the general strategies
and thinking are still relevant.

That said, if you are looking for details about specific technology, that
book is too outdated to be useful. Also, most of the architecture and
capacity planning he focuses on in that book is supplied by Cloud Foundry,
and utility/cloud computing in general. So, like reading Roy Fieldings'
REST paper, it could help you learn some of the fundamentals present in
many internet systems. But it won't teach you practical details about
tactical decisions you have to make regarding technology choices.

The other classic I associate with Cal's book is Martin Folwers "patterns
of enterprise architecture". The patterns themselves might be a little
rusty, but the overview sections cover the fundamental problems that most
web applications have to deal with, and how dealing with these problems
results in the architectures we now find standard and familiar. That
material is more focused on the kind of application development done on CF.

Sadly, I don't have a recommendation for a modern book on micro-services or
stateless front-end applications. Most books in this category are not
great, the advice is usually very shallow. I'd love to hear about a good
one.