1 Commits (5848d8a2b4e0c500c384bcbdcc84b5feec3f6549)

Author	SHA1	Message	Date
Martin Atkins	d0a35c60a7	providercache: Ignore lock-mismatching global cache entries ... When we originally introduced the trust-on-first-use checksum locking mechanism in v0.14, we had to make some tricky decisions about how it should interact with the pre-existing optional read-through global cache of provider packages: The global cache essentially conflicts with the checksum locking because if the needed provider is already in the cache then Terraform skips installing the provider from upstream and therefore misses the opportunity to capture the signed checksums published by the provider developer. We can't use the signed checksums to verify a cache entry because the origin registry protocol is still using the legacy ziphash scheme and that is only usable for the original zipped provider packages and not for the unpacked-layout cache directory. Therefore we decided to prioritize the existing cache directory behavior at the expense of the lock file behavior, making Terraform produce an incomplete lock file in that case. Now that we've had some real-world experience with the lock file mechanism, we can see that the chosen compromise was not ideal because it causes "terraform init" to behave significantly differently in its lock file update behavior depending on whether or not a particular provider is already cached. By robbing Terraform of its opportunity to fetch the official checksums, Terraform must generate a lock file that is inherently non-portable, which is problematic for any team which works with the same Terraform configuration on multiple different platforms. This change addresses that problem by essentially flipping the decision so that we'll prioritize the lock file behavior over the provider cache behavior. Now a global cache entry is eligible for use if and only if the lock file already contains a checksum that matches the cache entry. This means that the first time a particular configuration sees a new provider it will always be fetched from the configured installation source (typically the origin registry) and record the checksums from that source. On subsequent installs of the same provider version already locked, Terraform will then consider the cache entry to be eligible and skip re-downloading the same package. This intentionally makes the global cache mechanism subordinate to the lock file mechanism: the lock file must be populated in order for the global cache to be effective. For those who have many separate configurations which all refer to the same provider version, they will need to re-download the provider once for each configuration in order to gather the information needed to populate the lock file, whereas before they would have only downloaded it for the _first_ configuration using that provider. This should therefore remove the most significant cause of folks ending up with incomplete lock files that don't work for colleagues using other platforms, and the expense of bypassing the cache for the first use of each new package with each new configuration. This tradeoff seems reasonable because otherwise such users would inevitably need to run "terraform providers lock" separately anyway, and that command _always_ bypasses the cache. Although this change does decrease the hit rate of the cache, if we subtract the never-cached downloads caused by "terraform providers lock" then this is a net benefit overall, and does the right thing by default without the need to run a separate command.	4 years ago