dws2jgf: add script for generating rabbit map

Problem: as described in #193, JGF is too unwieldy to be stored in
Ansible. On the other hand, Flux's ability to start up and run
jobs cannot be dependent on the responsiveness of kubernetes, so
generating JGF from kubernetes before starting Flux is not an
option.

A solution would be to store some static rabbit data in ansible,
generated by reading from kubernetes. This data could be read in
to generate JGF.

Add a script that generates a JSON file describing which nodes map
to which rabbits and what the capacity of each rabbit is.

src/cmd/Makefile.am

@@ -1,2 +1,3 @@
 dist_fluxcmd_SCRIPTS = \
-	flux-dws2jgf.py
+	flux-dws2jgf.py \
+	flux-rabbitmapping.py

src/cmd/flux-rabbitmapping.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+
+import argparse
+import sys
+import json
+import subprocess
+
+import flux
+from flux.hostlist import Hostlist
+
+import kubernetes as k8s
+from kubernetes.client.rest import ApiException
+
+
+def get_storage(config_file):
+    k8s_client = k8s.config.new_client_from_config(config_file=config_file)
+    try:
+        api_instance = k8s.client.CustomObjectsApi(k8s_client)
+    except ApiException as rest_exception:
+        if rest_exception.status == 403:
+            raise Exception(
+                "You must be logged in to the K8s or OpenShift cluster to continue"
+            )
+        raise
+
+    group = "dataworkflowservices.github.io"
+    version = "v1alpha2"
+    plural = "storages"
+    return api_instance.list_cluster_custom_object(group, version, plural)
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        formatter_class=flux.util.help_formatter(),
+        description=("Create a mapping between compute nodes and rabbit nodes"),
+    )
+    parser.add_argument(
+        "--kubeconfig",
+        "-k",
+        default=None,
+        metavar="FILE",
+        help="Path to kubeconfig file to use",
+    )
+    parser.add_argument(
+        "--indent",
+        "-i",
+        default=None,
+        type=int,
+        metavar="N",
+        help="Number of spaces to indent output JSON document",
+    )
+    parser.add_argument(
+        "--nosort",
+        action="store_false",
+        help="Do not sort keys in output JSON document",
+    )
+    args = parser.parse_args()
+    rabbit_mapping = {"computes": {}, "rabbits": {}}
+    for nnf in get_storage(args.kubeconfig)["items"]:
+        hlist = Hostlist()
+        nnf_name = nnf["metadata"]["name"]
+        for compute in nnf["status"]["access"].get("computes", []):
+            hlist.append(compute["name"])
+            rabbit_mapping["computes"][compute["name"]] = nnf_name
+        rabbit_mapping["rabbits"][nnf_name] = {}
+        rabbit_mapping["rabbits"][nnf_name]["hostlist"] = hlist.uniq().encode()
+        rabbit_mapping["rabbits"][nnf_name]["capacity"] = nnf["status"]["capacity"]
+    json.dump(rabbit_mapping, sys.stdout, indent=args.indent, sort_keys=args.nosort)
+
+
+if __name__ == "__main__":
+    main()