Update release image location calculation docs
@@ -349,6 +349,37 @@ tags:
### Calculation of docker image location for releases
+The release image locations are comprised of multiple elements: the docker registry URL, the organization and repository, the stemcell name and version, the fissile version and the release name and version. Release image locations always have to be resolved in the context of an instance group/job because it depends on the stemcell that is being used.
+
+A typical release image location looks could look like `hub.docker.com/cfcontainerization/cflinuxfs3-release:opensuse-15.0-28.g837c5b3-30.263-7.0.0_233.gde0accd0-0.62.0`.
+
+The different elements are taken from different places in the manifest. Given this excerpt from a BOSH deployment manifest:
+
+```yaml
+stemcells:
+- alias: default
+ os: opensuse-42.3
+ version: 28.g837c5b3-30.263-7.0.0_234.gcd7d1132
+instance_groups:
+- name: diego-cell
+ stemcell: default
+ jobs:
+ - name: cflinuxfs3-rootfs-setup
+ release: cflinuxfs3
+releases:
+- name: cflinuxfs3
+ version: 0.62.0
+ url: hub.docker.com/cfcontainerization
+ sha1: 6466c44827c3493645ca34b084e7c21de23272b4
+ stemcell:
+ os: opensuse-15.0
+ version: 28.g837c5b3-30.263-7.0.0_233.gde0accd0
+```
+
+the stemcell information (name, and stemcell and fissile version) are taken from the `stemcells` entry that matches the instance group's stemcell alias. The registry URL including the organization, the release name, and the version com from the `releases` entry that's referenced from the job.
+
+*Note*: Releases can optionally specify a separate `stemcell` section, in which case the information from the instance group stemcell is overridden.
+
### Variables to Extended Secrets
For each **BOSH Variable**, the cf-operator creates `ExtendedSecrets`.
