Distribute the hosts to be crawled by MM2 between the existing crawlers

This commit adds two new scripts to the crawlers:
 * mm2_get-highest-active-host-id: this queries the MM database and returns
   the id of the active mirror with the highest id
 * run_crawler.sh: this calculates the right startid and stopid parameters
   depending on the number of available crawlers

These scripts are integrated into the start of the crawler so that each
crawler only crawls a subset of the existing mirrors. This distribution
is not perfect as it pretends that the active mirrors are equally
distributed under the total number of existing mirrors.

roles/mirrormanager/crawler/files/crawler.cron

@@ -1,4 +1,4 @@
 # run the crawler twice a day
 # logs sent to /var/log/mirrormanager/crawler.log and crawl/* by default
-# 32GB of RAM is not enough for 75 threads, 40 seems to work so far
+# 32GB of RAM is not enough for 75 threads, 35 seems to work so far
-0 */12 * * * mirrormanager /usr/bin/mm2_crawler --threads 40 > /dev/null 2>&1
+0 */12 * * * mirrormanager /usr/bin/mm2_crawler --threads 35 `/usr/local/bin/run_crawler.sh 2` > /dev/null 2>&1

roles/mirrormanager/crawler/files/mm2_get-highest-active-host-id

@@ -0,0 +1,32 @@
+#!/usr/bin/python
+
+import argparse
+import sys
+
+import mirrormanager2.lib
+
+parser = argparse.ArgumentParser(usage=sys.argv[0] + " [options]")
+parser.add_argument(
+    "-c", "--config",
+    dest="config", default='/etc/mirrormanager/mirrormanager2.cfg',
+    help="Configuration file to use")
+
+options = parser.parse_args()
+
+config = dict()
+with open(options.config) as config_file:
+    exec(compile(config_file.read(), options.config, 'exec'), config)
+
+session = mirrormanager2.lib.create_session(config['DB_URL'])
+
+# Get all active mirrors
+hosts = mirrormanager2.lib.get_mirrors(session, private=False,
+    admin_active=True, user_active=True, site_private=False,
+    site_user_active=True, site_admin_active=True)
+
+# only the ids
+hosts = [ host.id for host in hosts ]
+
+session.close()
+
+print max(hosts)

roles/mirrormanager/crawler/files/run_crawler.sh

@@ -0,0 +1,29 @@
+#/bin/bash
+
+if [ $# -ne 1 ]; then
+        exit 0
+fi
+
+NUMBER_OF_CRAWLERS=$1
+HOST=`hostname -s`
+MAX_HOST=`/usr/local/bin/mm2_get-highest-active-host-id`
+
+# make MAX_HOST a multiple of NUMBER_OF_CRAWLERS
+let FIX=${MAX_HOST}%${NUMBER_OF_CRAWLERS}
+
+if [ "${FIX}" -ne "0" ]; then
+        let MAX_HOST=${MAX_HOST}+${NUMBER_OF_CRAWLERS}-${FIX}
+fi
+
+let PART=${MAX_HOST}/${NUMBER_OF_CRAWLERS}
+
+STARTID=0
+STOPID=${PART}
+
+for i in `seq 1 ${NUMBER_OF_CRAWLERS}`; do
+        if [ "${HOST}" == "mm-crawler0${i}" ]; then
+                echo "--startid=${STARTID} --stopid=${STOPID}"
+        fi
+        let STARTID=${STARTID}+${PART}
+        let STOPID=${STOPID}+${PART}
+done

roles/mirrormanager/crawler/tasks/main.yml

@@ -51,3 +51,9 @@
     setype=httpd_sys_content_t
     state=directory
     recurse=yes
+
+- name: install the script to get the highest mirror id
+  copy: src=mm2_get-highest-active-host-id dest=/usr/local/bin/mm2_get-highest-active-host-id mode=0755
+
+- name: install the crawler distribute script
+  copy: src=run_crawler.sh dest=/usr/local/bin/run_crawler.sh mode=0755