launch: add ssh keys to inventory

When bringing up a new server, scan the ssh-keys of the remote IP and
add them automatically to the inventory output.

c.f. I4863425d5b784d0cdf118e1252414ca78fd24179

Change-Id: I2120fd476aa89e207ab76a1fc0faeeb5a0fb55ce

launch/src/opendev_launch/dns.py

@@ -21,6 +21,7 @@
 import argparse
 from . import rax_rdns
 from .sshfp import sshfp_print_records
+from .ssh_knownhosts import generate_known_hosts
 
 
 def get_href(server):
@@ -70,6 +71,8 @@ def set_rax_reverse_dns(cloud, server, ip4, ip6):
 
 
 def print_inventory_yaml(server, ip4, ip6):
+    known_hosts = generate_known_hosts(ip4)
+
     print("\n")
     print("Put the following into system-config:inventory/base/hosts.yaml")
     print("\n")
@@ -82,6 +85,9 @@ def print_inventory_yaml(server, ip4, ip6):
     print("      public_v4: {ip4}".format(ip4=ip4))
     if ip6:
         print("      public_v6: {ip6}".format(ip6=ip6))
+    print("      host_keys:")
+    for (key, fingerprint) in known_hosts:
+        print("        - '%s %s'" % (key, fingerprint))
 
 
 def main():

launch/src/opendev_launch/ssh_knownhosts.py

@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+import argparse
+import subprocess
+
+def generate_known_hosts(ip):
+    '''Given an IP address (hostname not in dns yet), scan and return
+    inventory known_hosts strings
+    '''
+
+    p = ['ssh-keyscan', ip]
+    s = subprocess.run(p,
+                       stdout=subprocess.PIPE,
+                       stderr=subprocess.PIPE).stdout.decode('utf-8')
+    known_hosts = []
+    for line in s.split('\n'):
+        if not line:
+            continue
+        if line.startswith('#'):
+            continue
+        _, key_type, fingerprint = line.split(' ')
+        known_hosts.append((key_type, fingerprint))
+
+    return known_hosts
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("ip", help="address to scan")
+    args = parser.parse_args()
+
+    known_hosts = generate_known_hosts(args.ip)
+    for (host, fingerprint) in known_hosts:
+        print("%s %s" % (host, fingerprint))
+
+if __name__ == '__main__':
+    main()