Download size of Docker images

Question

While pulling a Docker image, it downloads it in separate parts (layers). I need to get the download size of all necessary layers of an image before actually downloading it.

Is there a way to do it?

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One can just be running the docker pull command and watch the output:

ffcacfbccecb: Downloading [+++++>    ] 14.1 MB/30.13 MB
ffcdbdebabbe: Downloading [++>       ] 1.1 MB/12.02 MB

So its download size is "42.15".

However I've got some options enabled to download layers one by one:

ffcacfbccecb: Downloading [+++++>    ] 14.1 MB/30.13 MB
ffcdbdebabbe: Waiting

So this solution doesn't work for me.

Answer 1

Unfortunately, the Docker Hub API isn't documented publicly. But you can get a JWT to use for the API and then make a call to list out the tags to get the size. Here is an example using jq to parse out the size in bytes:

First authenticate to get your token:

export HUBUSER=andyshinn
export HUBPASS=mypass
export HUBTOKEN=$(curl -s -H "Content-Type: application/json" -X POST -d '{"username": "'${HUBUSER}'", "password": "'${HUBPASS}'"}' https://hub.docker.com/v2/users/login/ | jq -r .token)

Now you can query the tags API to filter for a specific tag and get the size. In this example, we are getting the official library wordpress image and filtering out the latest tag:

curl -s -H "Authorization: JWT ${TOKEN}" "https://hub.docker.com/v2/repositories/library/wordpress/tags/?page_size=100" | jq -r '.results[] | select(.name == "latest") | .images[0].size'

You should get back something like 169817871 which is the size of the entire image in bytes. This is a modified example from information found at https://gist.github.com/kizbitz/e59f95f7557b4bbb8bf2.