There really is no one answer, and you're so right that scale is one of the determining factors. Sophisticated tools like Signadot are designed to help dozens of developers use one high-accuracy shared cluster, but that makes no sense if your team is small enough to Slack 'hey I'm going to push my stuff to Staging, no one change anything' for your testing phase :)
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I will just say that I published a follow up article that proposes some solutions.
https://thenewstack.io/how-to-shift-testing-left-4-tactical-...
There really is no one answer, and you're so right that scale is one of the determining factors. Sophisticated tools like Signadot are designed to help dozens of developers use one high-accuracy shared cluster, but that makes no sense if your team is small enough to Slack 'hey I'm going to push my stuff to Staging, no one change anything' for your testing phase :)