How does resource_class apply to multiple docker images?

Build Environment
1

The documentation describes the resources available to the docker executor and how to request more/fewer resources.

If I have a build that starts multiple docker images (similar to the config snippet below), are the 2 vCPUs and 4gb RAM shared between them? If not, how are resources allocated?

jobs:
  build:
    docker:
       - image: circleci/ruby:2.4.3-node-browsers
       - image: redis
       - image: vault:latest
       - image: {private_image_1}
       - image: {private_image_2}
2

resource_class is for the host container as a whole, so all images in a single job are going to be affected by those shared limits.

3

Ah, I thought the secondary images ran on other host(s), and so the resource limit could not easily be applied to these (or would have to be applied separately)?

4

Nope, all Docker images for the job are running in the same cgroup on the host.

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