[erlang-questions] 'ssl_otp_session_cache' ets table

Ingela Andin <>
Fri Nov 7 09:37:32 CET 2014


Hi!

Which version of the ssl application are you using? The session cleanup was
broken in one of the older versions.

Regards Ingela Erlang/OTP - team Ericsson AB

2014-11-06 17:20 GMT+01:00 Bogdan Andu <>:

> yes,
>
> in function ssl_manager:invalidate_session/4, the call
>
> erlang:send_after(delay_time(), self(), {delayed_clean_session, Key}),
> does the actual deletion of session from cache
>
> where delay_time/0 function returns ?CLEAN_SESSION_DB by default, which
> is 60 seconds
>
>
>
>
> On Thu, Nov 6, 2014 at 4:51 PM, Ingela Andin <>
> wrote:
>
>> Hi!
>>
>>
>> 2014-11-06 14:39 GMT+01:00 Bogdan Andu <>:
>>
>>> Hi,
>>>
>>> i have tried to pass to execute th following forms of commands:
>>>
>>> erl  -ssl session_lifetime 60
>>>
>>> erl  -ssl session_lifetime '60'
>>>
>>> erl  -ssl session_lifetime '[60]'
>>>
>>>
>>> in order to set a ssl session_lifetime of 60 seconds.
>>>
>>> in init of ssl_manager , after session_lifetime + 5 seconds a process is
>>> created to validate or invalidate sessions.
>>> So, after 65 seconds a foldl is called on sessions table to check
>>> sessions after formula:
>>> Now - TimeStamp < LifeTime
>>>
>>> However, even after I stop the client, the table 'ssl_otp_session_cache'
>>> 's size remains the same.
>>>
>>>
>>> After that once every ?CLEAN_SESSION_DB which is 60 seconds , the table
>>> is sweeped to delete any expired sessions,
>>>
>>> but also nothing happens.
>>>
>>>
>> There is also a delay in the actual deletion. In the first sweep the
>> sessions will only be invalidated as there may already be
>> spawned connection handlers that needs to read the session data before we
>> may delete it. It is a performance trade off.
>>
>> Regards Ingela Erlang/OTP team - Ericsson AB
>>
>>
>>
>>>
>>> On Thu, Nov 6, 2014 at 12:28 PM, Ingela Andin <>
>>> wrote:
>>>
>>>> Hi!
>>>>
>>>>
>>>> 2014-11-06 8:53 GMT+01:00 Bogdan Andu <>:
>>>>
>>>>> Hi,
>>>>>
>>>>> on my production servers I have relayd (on OpenBSD) daemon as a
>>>>> reverse proxy to some webservers
>>>>> where one can fine tune some connection parameters, as well as some
>>>>> ssl parameters.
>>>>>
>>>>> I give a snippet from a relayd.conf configuration file on one of my
>>>>> production server:
>>>>>
>>>>> .............
>>>>> #
>>>>> # Relay and protocol for HTTP layer 7 loadbalancing and SSL
>>>>> acceleration
>>>>> #
>>>>> http protocol www_ssl_prot {
>>>>>         header append "$REMOTE_ADDR" to "X-Forwarded-For"
>>>>>         header append "$SERVER_ADDR:$SERVER_PORT" to "X-Forwarded-By"
>>>>>         header change "Connection" to "close"
>>>>>
>>>>>         response header change "Server" to "Apache 0.1"
>>>>>
>>>>>         # Various TCP performance options
>>>>>         tcp { nodelay, sack, socket buffer 65536, backlog 128 }
>>>>>
>>>>>         ssl { no sslv2, no sslv3, tlsv1, ciphers "HIGH" }
>>>>>         ssl session cache disable
>>>>> }
>>>>>
>>>>> the last directive tells relayd not to use ssl cache.
>>>>>
>>>>> This configuration is working for years and relayd was restarted once
>>>>> by accident - my fault.
>>>>>
>>>>> SO, y question is:
>>>>>
>>>>> can we have this configurable in Erlang, in other words, we might be
>>>>> able to start an erlang vm such as:
>>>>>
>>>>> erl -ssl session_cache 'disable' -name  ....
>>>>>
>>>>> The ssl option session_cache can be set to disabled by default and can
>>>>> take values either disable or enabled.
>>>>>
>>>>>
>>>>>
>>>> You can already disable the reuse of the sessions using the server
>>>> option *{reuse_sessions, boolean()}* which default to true.
>>>> The thing we plan to do is to have a configurable limit on the table
>>>> size when sessions are reused.
>>>>
>>>> Regards Ingela Erlang/OTP team Ericsson AB
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>> Just to let you know...
>>>>>
>>>>> The statistics of a node running from yesterday when  I opened this
>>>>> thread of discussion, using a single client:
>>>>>
>>>>> Node: '' (Connected) (17/6.2) unix (openbsd 5.4.0) CPU:2
>>>>> SMP +A:10
>>>>> Time: local time 09:48:48, up for 000:20:27:49, 0ms latency,
>>>>> Processes: total 681 (RQ 0) at 610275 RpI using 11526.4k (11805.8k
>>>>> allocated)
>>>>> Memory: Sys 94835.5k, Atom 407.7k/419.5k, Bin 176.4k, Code 9934.7k,
>>>>> Ets 80739.2k
>>>>>
>>>>> ...........
>>>>>
>>>>> So, can be this made configurable?
>>>>>
>>>>>
>>>>>
>>>>> On Wed, Nov 5, 2014 at 8:52 PM, Ingela Andin <>
>>>>> wrote:
>>>>>
>>>>>> Hi!
>>>>>>
>>>>>> 2014-11-05 14:15 GMT+01:00 Tony Rogvall <>:
>>>>>>
>>>>>>> I think the ssl session times is the problem here, and the lack of a
>>>>>>> maximum size.
>>>>>>>
>>>>>>> You can change the session time in the ssl environment:
>>>>>>> session_lifetime
>>>>>>> The default is set to 24 hours (in seconds) (if I read it correctly,
>>>>>>> in ssl_manager.erl)
>>>>>>>
>>>>>>
>>>>>> Default values are always hard. It is the maximum recommended time
>>>>>> for a session to live
>>>>>> according to the spec.
>>>>>>
>>>>>>
>>>>>>> I guess that a session_cache_size could be a nice thing to have,
>>>>>>> limiting the growth of the session cache.
>>>>>>>
>>>>>>>
>>>>>> Yes I agree.
>>>>>>
>>>>>>
>>>>>>> In other words you have to estimate the life time of your clients and
>>>>>>> try to find a reasonable session_lifetime to match that, without
>>>>>>> blowing up
>>>>>>> the system.
>>>>>>>
>>>>>>> Maybe the ssl_session_cache_api could be used to implement a
>>>>>>> strategy with a max size
>>>>>>> cache. Retire session least recently used, while performing the
>>>>>>> update?
>>>>>>> There is a time_stamp in the session that that could be used for
>>>>>>> this purpose.
>>>>>>>
>>>>>>> OTP: Why is a fixed limit not implemented in the standard
>>>>>>> ssl_session_cache?
>>>>>>> Could this be a target for DOS attacks?
>>>>>>>
>>>>>>
>>>>>>
>>>>>> We are aware of the problem, and it is on our todo list. One reason
>>>>>> it has not had top priority is that on the server side there are often
>>>>>> other mechanisms
>>>>>> like firewalls and webbserver settings that limits the problem.  And
>>>>>> the reason why it was not implemented in the first place is that
>>>>>> implementations by nature
>>>>>> are iterative and at first you are faced with a lot of bigger
>>>>>> problems to solve and then you need to iterate and fine tune and fix things
>>>>>> that you now have a better understanding of.
>>>>>>
>>>>>> In current master there is a change to the session table that limits
>>>>>> the growth on the client side if the client behaves inappropriate. It also
>>>>>> splits the session table into
>>>>>> a server and a client table which is a better implementation as the
>>>>>> same Erlang node can be both a client and a server at the same time. So if
>>>>>>  someone feels like contributing a max limit please base it on the master
>>>>>>  branch, otherwise I suspect someone compiling about it did raise the
>>>>>> priority level  a little.
>>>>>>
>>>>>>
>>>>>> Regards Ingela Erlang/OTP team - Ericsson AB
>>>>>>
>>>>>>
>>>>>>
>>>>>>> /Tony
>>>>>>>
>>>>>>> > On 5 nov 2014, at 13:08, Bogdan Andu <> wrote:
>>>>>>> >
>>>>>>> >
>>>>>>> >
>>>>>>> > Hi,
>>>>>>> >
>>>>>>> > I performed a series of test regarding the an Erlang SSL server.
>>>>>>> >
>>>>>>> > In this setup a major role is played by the table called
>>>>>>> 'ssl_otp_session_cache', and of course the processes using it.
>>>>>>> >
>>>>>>> > The problem is that the size of table increases constantly and,
>>>>>>> because an ets table does not automatically deallocate memory unless the
>>>>>>> object are deleted from that table, the size of table remains the same even
>>>>>>> if there no ssl connections to server.
>>>>>>> >
>>>>>>> > For example, with a single client running 'ad infinitum' the table
>>>>>>> increases at a rate of 5 MBytes/hour. In 12 hours there are allocate around
>>>>>>> 60 MB of memory only for this table.
>>>>>>> >
>>>>>>> > Some info about this:
>>>>>>> > $ erl -sname  -remsh  -setcookie
>>>>>>> operator
>>>>>>> > Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:2:2]
>>>>>>> [async-threads:10] [kernel-poll:false]
>>>>>>> >
>>>>>>> > Eshell V6.2  (abort with ^G)
>>>>>>> >
>>>>>>> >
>>>>>>> > ()1> ets:i().
>>>>>>> >  id              name              type  size   mem      owner
>>>>>>> >
>>>>>>> ----------------------------------------------------------------------------
>>>>>>> >  12              cookies           set   0      291      auth
>>>>>>> >  4111            code              set   410    26132
>>>>>>> code_server
>>>>>>> >  8208            code_names        set   58     7459
>>>>>>>  code_server
>>>>>>> >  12307           httpc_manager__session_cookie_db bag   0
>>>>>>> 291      httpc_manager
>>>>>>> >  16404           ssl_otp_cacertificate_db set   0      291
>>>>>>> ssl_manager
>>>>>>> >  20501           ssl_otp_ca_file_ref set   0      291
>>>>>>> ssl_manager
>>>>>>> >  24598           ssl_otp_pem_cache set   3      360
>>>>>>> ssl_manager
>>>>>>> >  28695           ssl_otp_session_cache ordered_set 138057 8421893
>>>>>>> ssl_manager
>>>>>>> >  32797           dets              duplicate_bag 2      308
>>>>>>> dets
>>>>>>> >  40990           ign_requests      set   0      291
>>>>>>> inet_gethost_native
>>>>>>> >  45087           ign_req_index     set   0      291
>>>>>>> inet_gethost_native
>>>>>>> >  2261635104      shell_records     ordered_set 0      81
>>>>>>>  <0.30638.37>
>>>>>>> >  ac_tab          ac_tab            set   33     2216
>>>>>>>  application_controller
>>>>>>> >  code_map        code_map          set   100    2791     <0.72.0>
>>>>>>> >  config          config            set   12     892      <0.72.0>
>>>>>>> >  dets_owners     dets_owners       set   1      298      dets
>>>>>>> >  dets_registry   dets_registry     set   1      299      dets
>>>>>>> >  file_io_servers file_io_servers   set   1      344
>>>>>>> file_server_2
>>>>>>> >  global_locks    global_locks      set   0      291
>>>>>>> global_name_server
>>>>>>> >  global_names    global_names      set   0      291
>>>>>>> global_name_server
>>>>>>> >  global_names_ext global_names_ext  set   0      291
>>>>>>> global_name_server
>>>>>>> >  global_pid_ids  global_pid_ids    bag   0      291
>>>>>>> global_name_server
>>>>>>> >  global_pid_names global_pid_names  bag   0      291
>>>>>>> global_name_server
>>>>>>> >  httpc_manager__handler_db httpc_manager__handler_db set   0
>>>>>>> 291      httpc_manager
>>>>>>> >  httpc_manager__session_db httpc_manager__session_db set   0
>>>>>>> 291      httpc_manager
>>>>>>> >  inet_cache      inet_cache        bag   0      291      inet_db
>>>>>>> >  inet_db         inet_db           set   29     600      inet_db
>>>>>>> >  inet_hosts_byaddr inet_hosts_byaddr bag   0      291      inet_db
>>>>>>> >  inet_hosts_byname inet_hosts_byname bag   0      291      inet_db
>>>>>>> >  inet_hosts_file_byaddr inet_hosts_file_byaddr bag   0      291
>>>>>>>   inet_db
>>>>>>> >  inet_hosts_file_byname inet_hosts_file_byname bag   0      291
>>>>>>>   inet_db
>>>>>>> >  models          models            set   3      28952    <0.72.0>
>>>>>>> >  sys_dist        sys_dist          set   1      334      net_kernel
>>>>>>> > ok
>>>>>>> > ()5> ets:info(ssl_otp_session_cache).
>>>>>>> > undefined
>>>>>>> > ()7> (8421893*8)/1024.
>>>>>>> > 65796.0390625
>>>>>>> > ()8> memory().
>>>>>>> > [{total,92699464},
>>>>>>> >  {processes,8964000},
>>>>>>> >  {processes_used,8963152},
>>>>>>> >  {system,83735464},
>>>>>>> >  {atom,429569},
>>>>>>> >  {atom_used,421768},
>>>>>>> >  {binary,199040},
>>>>>>> >  {code,10411520},
>>>>>>> >  {ets,69163032}]
>>>>>>> >
>>>>>>> > The memory allocated to table 'ssl_otp_session_cache' is roughly
>>>>>>> 64 MB in 12 hours.
>>>>>>> >
>>>>>>> > On an OpenBSD platform such process gets killed immediately it
>>>>>>> hits some memory and/or CPU limits.
>>>>>>> >
>>>>>>> > To make this test on OpenBSD I had to put 'infinit' to memory,
>>>>>>> otherwise the Erlang VM would be killed.
>>>>>>> >
>>>>>>> > How can one control , tweak or configure this table such that it
>>>>>>> does not accumulate such data at such high rate.
>>>>>>> >
>>>>>>> > I seems the table being created private, and there is no way to
>>>>>>> ets:delete_all_objects/1 from table manually.
>>>>>>> >
>>>>>>> > I know that this table caches some SSL data related to clients,
>>>>>>> but the client has the same IP address,
>>>>>>> > and I wonder why is neccesary to store a lot of SSL connection
>>>>>>> info about the same client when only the ephemeral peer port
>>>>>>> > differs?
>>>>>>> >
>>>>>>> > How the size of this table can be held in reasonable limits and
>>>>>>> the rate it's size increases ?
>>>>>>> >
>>>>>>> > Please if somebody shed some light on these issues.
>>>>>>> >
>>>>>>> > Thank you,
>>>>>>> >
>>>>>>> > Bogdan
>>>>>>> >
>>>>>>> >
>>>>>>> > _______________________________________________
>>>>>>> > erlang-questions mailing list
>>>>>>> > 
>>>>>>> > http://erlang.org/mailman/listinfo/erlang-questions
>>>>>>>
>>>>>>> "Installing applications can lead to corruption over time.
>>>>>>> Applications gradually write over each other's libraries, partial upgrades
>>>>>>> occur, user and system errors happen, and minute changes may be
>>>>>>> unnoticeable and difficult to fix"
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> erlang-questions mailing list
>>>>>>> 
>>>>>>> http://erlang.org/mailman/listinfo/erlang-questions
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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