CODEWITHSUNDEEP
dockerdocker-registry
danny
danny

Reputation: 10473

Docker cache confusion

I'm confused about some docker cache behavior I'm seeing.

First I do a docker build, then push the image to a repository, and then I delete all my docker data locally (I'm running docker in a VM on OSX, so I destroy and re-create the VM). Then I pull the image that I just pushed to the repository.

Now, I make any change at all to my code, e.g. add a newline to the README. When I run docker build, none of the steps are cached. It runs all the steps one by one from the beginning.

Of course, I would expect any COPY . step to be invalidated since I have updated the code, but even the steps before that are invalidated.

Why does this happen?

UPDATE:

Here's my output (anonymized a bit).

There are no command line arguments, this happens when I just run docker build .

Step 1 : FROM 123456.dkr.ecr.us-east-1.amazonaws.com/foo:0.1.1 0.1.1: foo d89e1bee20d9: Already exists 9e0bc8a71bde: Already exists 27aa681c95e5: Already exists a3ed95caeb02: Already exists 1f23dc7f328b: Already exists 7c5e36b70451: Already exists 0844dd833da6: Already exists 8017b7feecce: Already exists 0dd824b407cc: Already exists ecfa07005844: Already exists 697248412260: Already exists df6663ccf76d: Already exists Digest: sha256:823221727843f32d1a52879aa57e40e02f4db2b31a2344384fc0307fa85c2b52 Status: Downloaded newer image for 123456.dkr.ecr.us-east-1.amazonaws.com/foo:0.1.1 ---> b6b907685beb Step 2 : RUN curl https://example.com > /file ---> Running in 1f912826e4c8 OK

Where it says that it "Downloaded newer image" for the "foo" base image, could that be where the problem is? As you can see, all the layers already exist at that point. So it's strange that it thinks it has downloaded a newer image, maybe that's related to why the following steps aren't cached?

Upvotes: 1

Views: 295

Answers (1)

saada
saada

Reputation: 2761

Deleting the VM also deletes all images pulled and built from your terminal. This includes cached layers. This is expected behavior since Docker is not actually running in your host machine (OS X). Docker Engine is actually running inside the VM and your Docker client CLI is talking to Engine via an API. Think of your VM as a Docker server and your CLI as a Docker client. Because Docker Engine runs in the VM; the cached layers, pulled images, and all other data stored in the VM will be deleted along with the VM when you delete it.

Upvotes: 1

Related Questions