How to understand if you need to use expires headers

Key quotes:

• "Some AWS users, including me, use S3 to host static website and CloudFront for two reasons: Well, a good idea is setting a max-age equals to 10 years (more or less, this is not really very important) and when you update your website, you need to invalidate only the new files and objects."
• "Using AWS CLI, list the id of a given user: Create a new key: Now you should re-type the first command, you will notice that you have two keys: Disable the old one: Delete it: Another option to reduce costs that is not widely used but could be useful in some cases, is restricting the usage of your CloudFront files to certain countries."

Key quotes:

• "Setting up a CDN for your assets (CSS, JS, photos, SVGs, etc.) isn’t a silver bullet on its own, but it can dramatically speed up the load time of your site and if caching is used it can decrease the used bandwidth from the origin."
• "By default CloudFront caches objects for 24 hours on the edge nodes, but this behaviour can be modified in two ways: You can read more about how to set this up in the AWS documentation."
• "You can add meta tags to your objects for example cache-control max-age headers and S3 will respond with those headers to the CDN."
• "Do this on origin response this way we can cache the objects on the edge nodes when origin responds and we don’t need to execute our functions as many times as we would if we trigger the function on viewer response."
• "We have our function deployed, but it’s not being triggered, we still don’t see the cache-control headers."

Key quotes:

• "All browsers attempt to keep local copies of static assets in an effort to reduce page load times and minimize network traffic."
• "The browser won’t have any files cached for the site so it will fetch everything from the server."
• "The browser will retrieve the HTML page from the web server but consult its cache for the static assets (JavaScript, CSS, images)."
• "The browser inspects the headers of the HTTP response generated by the web server."
• "The server can include an ETag in its response, which the browser can then use this in a future request (after the file has expired) to determine if the cache contains a stale copy."
• "This tells the browser to cache the file but not to use it until it checks with the server to validate we have the latest version."

Key quotes:

• "The Cache-Control general-header field is used to specify directives for caching mechanisms in both requests and responses."
• "no-store means do not store particular resource from the server anywhere (i.e browser or proxy caching )."
• "max-age Specifies the maximum amount of time a resource will be considered fresh."
• "The content at this URL never changes then the browser/caching servers can cache this resource for a 365 days without a problem."
• "Cached content younger than max-age seconds can be used without consulting the server."
• "In this pattern, browser doesn’t believe the local resource state and always validates with server to check its freshness."

Key quotes:

• "What’s interesting, though, is that a few HTTP clients will still consider responses cacheable if they don’t see a no-cache in the Pragma, and so the best practice to avoid caching has been to send both Cache-Control and Pragma: At the same time, a peculiar use of Pragma is by telling HTTP/1.0 caches not to cache (via Pragma) while allowing HTTP/1.1 caches to do so (via Cache-Control): Enough with expiration: it’s now time to move on to validation, a more expensive but granular way to implement HTTP caching."