0.4 HTTPS, certificates and trust
You can diagnose a certificate error instead of clicking through it.
Before:nothing requiredUnlocks:01. Cloud Foundations
A certificate error is a message, and this topic teaches reading it instead of clicking through it: what a certificate authority actually vouches for, how chains and expiry work, and how Let's Encrypt made renewal automatic. It earns a slot in the groundwork because HTTPS fronts every service deployed later in the course. The common confusion is thinking a valid certificate means a trustworthy site — it only means the traffic is encrypted to the domain named, which is necessary, useful, and much less than trust.
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What a certificate authority actually vouches for
A certificate authority vouches that whoever presents a certificate controls the name on it, and nothing more than that. Knowing exactly how narrow that promise is prevents a lot of misplaced confidence.
Certificate chains, expiry and renewal
Trust is passed along a chain from a root the browser already trusts down to your server, and every certificate on that chain has an expiry date. Most outages here are somebody forgetting one of those dates.
Let's Encrypt and automated renewal
Free automated certificates changed the economics of encryption, and automatic renewal changed the failure mode from expensive to forgettable. This is the setup most small deployments should use.
Common browser errors and what each one means
Each certificate warning means something specific: wrong name, expired, untrusted issuer, or broken chain. Being able to read which one you are looking at is what lets you fix it rather than click past it.
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