Before, all backend implementations were required to return an error if
the file that is to be written already exists in the backend. For most
backends, that means making a request (e.g. via HTTP) and returning an
error when the file already exists.
This is not accurate, the file could have been created between the HTTP
request testing for it, and when writing starts. In addition, apart from
the `config` file in the repo, all other file names have pseudo-random
names with a very very low probability of a collision. And even if a
file name is written again, the way the restic repo is structured this
just means that the same content is placed there again. Which is not a
problem, just not very efficient.
So, this commit relaxes the requirement to return an error when the file
in the backend already exists, which allows reducing the number of API
requests and thereby the latency for remote backends.
During the development of #1524 I discovered that the Google Cloud
Storage backend did not yet use the HTTP transport, so things such as
bandwidth limiting did not work. This commit does the necessary magic to
make the GS library use our HTTP transport.
By default, the GCS Go packages have an internal "chunk size" of 8MB,
used for blob uploads.
Media().Do() will buffer a full 8MB from the io.Reader (or less if EOF
is reached) then write that full 8MB to the network all at once.
This behavior does not play nicely with --limit-upload, which only
limits the Reader passed to Media. While the long-term average upload
rate will be correctly limited, the actual network bandwidth will be
very spikey.
e.g., if an 8MB/s connection is limited to 1MB/s, Media().Do() will
spend 8s reading from the rate-limited reader (performing no network
requests), then 1s writing to the network at 8MB/s.
This is bad for network connections hurt by full-speed uploads,
particularly when writing 8MB will take several seconds.
Disable resumable uploads entirely by setting the chunk size to zero.
This causes the io.Reader to be passed further down the request stack,
where there is less (but still some) buffering.
My connection is around 1.5MB/s up, with nominal ~15ms ping times to
8.8.8.8.
Without this change, --limit-upload 1024 results in several seconds of
~200ms ping times (uploading), followed by several seconds of ~15ms ping
times (reading from rate-limited reader). A bandwidth monitor reports
this as several seconds of ~1.5MB/s followed by several seconds of
0.0MB/s.
With this change, --limit-upload 1024 results in ~20ms ping times and
the bandwidth monitor reports a constant ~1MB/s.
I've elected to make this change unconditional of --limit-upload because
the resumable uploads shouldn't be providing much benefit anyways, as
restic already uploads mostly small blobs and already has a retry
mechanism.
--limit-download is not affected by this problem, as Get().Download()
returns the real http.Response.Body without any internal buffering.
Updates #1216
If the service account used with restic does not have the
storage.buckets.get permission (in the "Storage Admin" role), Create
cannot use Get to determine if the bucket is accessible.
Rather than always trying to create the bucket on Get error, gracefully
fall back to assuming the bucket is accessible. If it is, restic init
will complete successfully. If it is not, it will fail on a later call.
Here is what init looks like now in different cases.
Service account without "Storage Admin":
Bucket exists and is accessible (this is the case that didn't work
before):
$ ./restic init -r gs:this-bucket-does-exist:/
enter password for new backend:
enter password again:
created restic backend c02e2edb67 at gs:this-bucket-does-exist:/
Please note that knowledge of your password is required to access
the repository. Losing your password means that your data is
irrecoverably lost.
Bucket exists but is not accessible:
$ ./restic init -r gs:this-bucket-does-exist:/
enter password for new backend:
enter password again:
create key in backend at gs:this-bucket-does-exist:/ failed:
service.Objects.Insert: googleapi: Error 403:
my-service-account@myproject.iam.gserviceaccount.com does not have
storage.objects.create access to object this-bucket-exists/keys/0fa714e695c8ecd58cb467cdeb04d36f3b710f883496a90f23cae0315daf0b93., forbidden
Bucket does not exist:
$ ./restic init -r gs:this-bucket-does-not-exist:/
create backend at gs:this-bucket-does-not-exist:/ failed:
service.Buckets.Insert: googleapi: Error 403:
my-service-account@myproject.iam.gserviceaccount.com does not have storage.buckets.create access to bucket this-bucket-does-not-exist., forbidden
Service account with "Storage Admin":
Bucket exists and is accessible: Same
Bucket exists but is not accessible: Same. Previously this would fail
when Create tried to create the bucket. Now it fails when trying to
create the keys.
Bucket does not exist:
$ ./restic init -r gs:this-bucket-does-not-exist:/
enter password for new backend:
enter password again:
created restic backend c3c48b481d at gs:this-bucket-does-not-exist:/
Please note that knowledge of your password is required to access
the repository. Losing your password means that your data is
irrecoverably lost.
In the manual, state which standard roles the service account must
have to work correctly, as well as the specific permissions required,
for creating even more specific custom roles.
