AWS Python Lambda with Oracle - OID Generation Failed

Question

I'm trying to connect to an Oracle DB using AWS Lambda Python code.

My code is below:

import sys, os
import cx_Oracle
import traceback

def main_handler(event, context):

  # Enter your database connection details here
  host = "server_ip_or_name"
  port = 1521
  sid = "server_sid"
  username = "myusername"
  password = "mypassword"

  try:
    dsn = cx_Oracle.makedsn(host, port, sid)
    print dsn
    connection = cx_Oracle.Connection("%s/%s@%s" % (username, password, dsn))
    cursor = connection.cursor()
    cursor.execute("select 1 / 0 from dual")
  except cx_Oracle.DatabaseError, exc:
    error, = exc.args
    print >> sys.stderr, "Oracle-Error-Code:", error.code
    print >> sys.stderr, "Oracle-Error-Message:", error.message
    tb = traceback.format_exc()
  else:
    tb = "No error"
  finally:
    print tb


if __name__ == "__main__":
  main_handler(sys.argv[0], None)

If have already added all dependencies in "lib" folder, thanks to AWS Python Lambda with Oracle

When running this code, I'm getting: DatabaseError: ORA-21561: OID generation failed

i've tried to connect using IP of the Oracle server and the name: same error.

Here is the output of the error

Oracle-Error-Code: 21561
Oracle-Error-Message: ORA-21561: OID generation failed

Traceback (most recent call last):
  File "/var/task/main.py", line 20, in main_handler
  connection = cx_Oracle.Connection("%s/%s@%s" % (username, password, dsn))
DatabaseError: ORA-21561: OID generation failed

For those who have successfully run the CX_Oracle in AWS Lambda Python, can you please help ?

Thanks

Answer 1

Ok, here is the explanation: Oracle has a funny behavior where if the hostname given by hostname can't be resolved, it will fail connecting to the DB. Fortunately, in Linux, one can override the DNS entry for a session by writing an alias file in /tmp, then setting the environment variable HOSTALIASES to that file.

So adding this code to my function help to generate this file, and now I can successfully connect:

f = open('/tmp/HOSTALIASES','w')
str_host = os.uname()[1]
f.write(str_host + ' localhost\n')
f.close()

Hope it can help someone else !

Answer 2

See the following other question for the resolution to this problem.

sqlplus remote connection giving ORA-21561

Effectively the client requires a host name in order to generate a unique identifier which is used when connecting to the database.

Answer 3

The accepted solution for this correct, but please also be aware that the HOSTALIASES mechanism does require working DNS (as strange as it sounds).

I struggled with this for a few hours having implemented the accepted solution and realised that I was not permitting outbound DNS on the security group attached to by Lambda function VPC interface (my connection was by IP address to Oracle DB, so initially did not think this was required).