Add patch property to allow arbitrary transforms as post-processing

Author: dln

README.md

@@ -150,6 +150,21 @@ Optionally mount an existing [Persistent Volume Claim](https://kubernetes.io/doc
 
 Override the working directory to run the command in, inside the container. The default is the build directory where the buildkite bootstrap and git checkout runs.
 
+### `patch` (optional, string)
+
+(Advanced / hack use). Provide a [jsonnet](https://jsonnet.org/) function to transform the resulting job manifest.
+
+Example:
+```
+function(job) job {
+  metadata: {
+    labels: job.metadata.labels {
+      foo: 'some extra label value',
+    },
+  },
+}
+```
+
 ## License
 
 Apache 2.0 (see [LICENSE](LICENSE))

hooks/command

@@ -22,10 +22,17 @@ function tail_logs {
 
 echo "--- :kubernetes: Starting Kubernetes Job ($(kubectl config current-context))"
 
+patchFunc="identity"
+if [[ -n "${BUILDKITE_PLUGIN_K8S_PATCH}" ]]; then
+  patchFunc=${BUILDKITE_PLUGIN_K8S_PATCH}
+fi
+export patchFunc
+
 jsonnet \
   --tla-str "jobName=${job_name}" \
   --tla-str-file "stepEnvFile=${BUILDKITE_ENV_FILE}" \
   --tla-code "agentEnv=$(jq -c -n env)" \
+  --tla-code patchFunc \
   "${basedir}/lib/job.jsonnet" \
   | kubectl apply -f -
 

lib/job.jsonnet

@@ -26,7 +26,9 @@ local allowedEnvs = std.set(
   ]
 );
 
-function(jobName, agentEnv={}, stepEnvFile='') {
+local identity = function(f) f;
+
+function(jobName, agentEnv={}, stepEnvFile='', patchFunc=identity) patchFunc({
   local env = {
     BUILDKITE_PLUGIN_K8S_SECRET_NAME: 'buildkite',
     BUILDKITE_PLUGIN_K8S_GIT_CREDENTIALS_SECRET_KEY: '',
@@ -236,4 +238,4 @@ function(jobName, agentEnv={}, stepEnvFile='') {
       },
     },
   },
-}
+})

plugin.yml

@@ -43,6 +43,8 @@ configuration:
       type: string
     workdir:
       type: string
+    patch:
+      type: string
   required:
   - image
   additionalProperties: false