Lukas Heeren ce61a1ed98 Adding ability to change max download attempts ... Moby works perfectly when you are in a situation when one has a good and stable internet connection. Operating in area's where internet connectivity is likely to be lost in undetermined intervals, like a satellite connection or 4G/LTE in rural area's, can become a problem when pulling a new image. When connection is lost while image layers are being pulled, Moby will try to reconnect up to 5 times. If this fails, the incompletely downloaded layers are lost will need to be completely downloaded again during the next pull request. This means that we are using more data than we might have to. Pulling a layer multiple times from the start can become costly over a satellite or 4G/LTE connection. As these techniques (especially 4G) quite common in IoT and Moby is used to run Azure IoT Edge devices, I would like to add a settable maximum download attempts. The maximum download attempts is currently set at 5 (distribution/xfer/download.go). I would like to change this constant to a variable that the user can set. The default will still be 5, so nothing will change from the current version unless specified when starting the daemon with the added flag or in the config file. I added a default value of 5 for DefaultMaxDownloadAttempts and a settable max-download-attempts in the daemon config file. It is also added to the config of dockerd so it can be set with a flag when starting the daemon. This value gets stored in the imageService of the daemon when it is initiated and can be passed to the NewLayerDownloadManager as a parameter. It will be stored in the LayerDownloadManager when initiated. This enables us to set the max amount of retries in makeDownoadFunc equal to the max download attempts. I also added some tests that are based on maxConcurrentDownloads/maxConcurrentUploads. You can pull this version and test in a development container. Either create a config `file /etc/docker/daemon.json` with `{"max-download-attempts"=3}``, or use `dockerd --max-download-attempts=3 -D &` to start up the dockerd. Start downloading a container and disconnect from the internet whilst downloading. The result would be that it stops pulling after three attempts. Signed-off-by: Lukas Heeren <lukas-heeren@hotmail.com> Signed-off-by: Sebastiaan van Stijn <github@gone.nl>		2019-09-19 13:51:40 +02:00
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dockerd	Adding ability to change max download attempts	2019-09-19 13:51:40 +02:00