* add dns query handling changes
* replace exception pass with error message
* simplify dns exception catching
* Add not set case to blacklist lookup result handling
The resolve method disables resolving relative names by default. This change probably makes a7710e90 unnecessary. @JoshData added some additional changes from query to resolve.
We were using duplicity 0.8.21-ppa202111091602~ubuntu1 from the duplicity PPA probably until June 5, which is when my box automatically updated to 0.8.23-ppa202205151528~ubuntu18.04.1. Starting with that version, two changes broke backups:
* The default s3 backend was changed to boto3. But boto3 depends on the AWS SDK which does not support Ubuntu 18.04, so we can't install it. Instead, we map s3: backup target URLs to the boto+s3 scheme which tells duplicity to use legacy boto. This should be reverted when we can switch to boto3.
* Contrary to the documentation, the s3 target no longer accepts a S3 hostname in the URL. It now reads the bucket from the hostname part of the URL. So we now drop the hostname from our target URL before passing it to duplicity and we pass the endpoint URL in a separate command-line argument. (The boto backend was dropped from duplicity's "uses_netloc" in 74d4cf44b1 (f5a07610d36bd242c3e5b98f8348879a468b866a_37_34), but other changes may be related.)
The change of target URL (due to both changes) seems to also cause duplicity to store cached data in a different directory within $STORAGE_ROOT/backup/cache, so on the next backup it will re-download cached manifest/signature files. Since the cache directory will still hold the prior data which is no longer needed, it might be a good idea to clear out the cache directory to save space. A system status checks message is added about that.
Fixes#2123
When building the part of the report about the current DS records founded, they are added in the same order as they were received when calling query_dns(), which can differ from run to run. This was making the difflib.SequenceMatcher() method to find the same line removed and added one line later, and sending an Status Checks Change Notice email with the same line added and removed when there was actually no real changes.
Port 465 with "implicit" (i.e. always-on) TLS is a more secure approach than port 587 with explicit (i.e. optional and only on with STARTTLS). Although we reject credentials on port 587 without STARTTLS, by that point credentials have already been sent.
* Stop generating RSASHA1-NSEC3-SHA1 keys on new installs since it is no longer recommended, but preserve the key on existing installs so that we continue to sign zones with existing keys to retain the chain of trust with existing DS records.
* Start generating ECDSAP256SHA256 keys during setup, the current best practice (in addition to RSASHA256 which is also ok). See https://www.iana.org/assignments/dns-sec-alg-numbers/dns-sec-alg-numbers.xhtml#dns-sec-alg-numbers-1 and https://www.cloudflare.com/dns/dnssec/ecdsa-and-dnssec/.
* Sign zones using all available keys rather than choosing just one based on the TLD to enable rotation/migration to the new key and to give the user some options since not every registrar/TLD supports every algorithm.
* Allow a user to drop a key from signing specific domains using DOMAINS= in our key configuration file. Signing the zones with extraneous keys may increase the size of DNS responses, which isn't ideal, although I don't know if this is a problem in practice. (Although a user can delete the RSASHA1-NSEC3-SHA1 key file, the other keys will be re-generated on upgrade.)
* When generating zonefiles, add a hash of all of the DNSSEC signing keys so that when the keys change the zone is definitely regenerated and re-signed.
* In status checks, if DNSSEC is not active (or not valid), offer to use all of the keys that have been generated (for RSASHA1-NSEC3-SHA1 on existing installs, RSASHA256, and now ECDSAP256SHA256) with all digest types, since not all registers support everything, but list them in an order that guides users to the best practice.
* In status checks, if the deployed DS record doesn't use a ECDSAP256SHA256 key, prompt the user to update their DS record.
* In status checks, if multiple DS records are set, only fail if none are valid. If some use ECDSAP256SHA256 and some don't, remind the user to delete the DS records that don't.
* Don't fail if the DS record uses the SHA384 digest (by pre-generating a DS record with that digest type) but don't recommend it because it is not in the IANA mandatory list yet (https://www.iana.org/assignments/ds-rr-types/ds-rr-types.xhtml).
See #1953
* Only spawn a thread pool when strictly needed
For --check-primary-hostname, the pool is not used.
When exiting, the other processes are left alive and will hang.
* Acquire pools with the 'with' statement
