[erlang-questions] 'ssl_otp_session_cache' ets table

Ingela Andin <>
Thu Nov 6 11:28:35 CET 2014


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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