Lately I've had to use jq a few times and got to understand the power of its pipe system. Here is an example of how to get the latest docker image tag in a specific docker repo of AWS ECR.
Firstly you have to know that aws ecr describe-images --repository-name $repo_name returns a json object which consists of a list of objects, each object looks like this:
{
"registryId": ...,
"repositoryName": ...,
"imageDigest": "sha256:...",
"imageTags": [
"..."
],
"imageSizeInBytes": ...,
"imagePushedAt": ...,
"imageManifestMediaType": "application/...",
"artifactMediaType": "application/..."
}
Not all objects have an imageTags.
Further requirements:
- I don't want objects that have a non-master-branch tag (they have "dev" in their tag)
- I am only interested in the first tag of each object
- I want to output the tag in a form that I can consume in a script later, in my case
REPO_NAME=tagwhereREPO_NAMEis an environment variable.
Here is the code:
aws ecr describe-images --repository-name $repo_name | jq '.[] | map(select(has("imageTags"))) | sort_by(.imagePushedAt) | map(select(.imageTags[0] | contains("dev") | not)) | .[-1] | [(.repositoryName | gsub("-";"_") | ascii_upcase), .imageTags[0]] | join("=")'
I explain each line (the following block of code will not run as-is due to the comments; use the above snippet instead):
repo_name=...
aws ecr describe-images --repository-name $repo_name |
# don't want quotes around the final output so -r:
jq -r '
# loop over all objects of the list:
.[]
# select those that have imageTags:
| map(select(has("imageTags")))
# filter out those that have "dev" in their tag:
| map(select(.imageTags[0] | contains("dev") | not))
# sort remaining ones by push date:
| sort_by(.imagePushedAt)
# keep only the most recent one
| .[-1]
# create pair based on fields of the selected object
| [
# 1st is env var name for the repo: all upper, and underscores:
(.repositoryName | gsub("-"; "_") | ascii_upcase),
# 2nd is the tag itself:
.imageTags[0]
]
# format items of the pair into ENV_VAR_NAME=tag:
| join("=")'
Example output:
MY_REPO_NAME=2021.03.22-9941301
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