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RMR Overview ============================================================================================ RMr Library ============================================================================================ NAME -------------------------------------------------------------------------------------------- RMr -- Ric Message Router Library DESCRIPTION -------------------------------------------------------------------------------------------- RMr is a library which provides a user application with the ability to send and receive messages to/from other RMr based applications without having to understand the underlying messaging transport environment (e.g. Nanomsg) and without needing to know which other endpoint applications are currently available and accepting messages. To do this, RMr depends on a routing table generated by an external source. This table is used to determine the destination endpoint of each message sent by mapping the message type T (supplied by the user application) to an endpoint entry. Once determined, the message is sent directly to the endpoint. The user application is unaware of which endpoint actually receives the message, and in some cases whether that message was sent to multiple applications. RMr functions do provide for the ability to respond to the specific source instance of a message allowing for either a request response, or call response relationship when needed. The Route Table ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The library must be given a route table which maps message numbers to endpoint groups such that each time a message of type T is sent, the message is delivered to one member of each group associated with T. For example, message type 2 might route to two different groups where group A consists of worker1 and worker2, while group B consists only of logger1. It is the responsibility of the route table generator to know which endpoints belong to which groups, and which groups accept which message types. Once understood, the route table generator publishes a table that is ingested by RMr and used for mapping messages to end points. The following is a simple route table which causes message types 0 through 9 to be routed to specific applications: :: newrt|start mse|0|-1| %meid mse|1|-1|app10:4560,app11:4560 mse|2|-1|app12:4560 mse|3|-1|app14:4560 mse|4|-1|app18:4560 mse|5|-1|app01:4560 mse|6|-1|app02:4560 mse|7|-1|app03:4560 mse|8|-1|app04:4560 mse|9|-1|app05:4560 newrt|end The special endpoint "%meid" indicates that the message type (0 in this case) is to be routed to the endpoint which has been listed as the "owner" for the meid appearing in the message. MEID ownership is communicated to RMR using the same Route Table Manager interface and by supplying a "table" such as the one below: :: meid_map | start mme_ar | control1 | meid000 meid001 meid002 meid003 meid004 meid005 mme_ar | control2 | meid100 meid101 meid102 meid103 meid_map | end | 2 This table indicates that the application (endpoint) *control1* "owns" 6 MEIDs and *control2* owns 4. When message type 0 is sent, the MEID in the message will be used to select the endpoint via this table. The MEID table will update the existing owner relationships, and add new ones; it is necessary to send only the changes with the add/replace (mme_ar) entries in the table. When necessary, MEIDs can be deleted by adding an mme_del record to the table. The following example illustrates how this might look: :: meid_map | start mme_ar | control1 | meid000 meid001 meid002 meid003 meid004 meid005 mme_ar | control2 | meid100 meid101 meid102 meid103 mme_del| meid200 meid401 meid_map | end | 3 Route Table Syntax ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The following illustrates the syntax for both the route table. :: newrt | start mse | [,] | [;]... newrt | end A round robin group is one or more endpoints from which one will be selected to receive the message. When multiple endpoints are given in a group, they must be separated with a comma. An endpoint is the IP address and port (e.g. 192.158.4.30:8219) or DNS name and port of the application that should receive the message type. If multiple round-robin groups are given, they must be separated by a semicolon, and MEID Map Syntax ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The MEID map is similar to the route table. Entries are used to add or replace the ownership of one or more MEIDs (mme_ar) or to delete one or more MEIDs (mme_del). The following is the syntax for the MEID map. :: meid_map | start mme_ar | | [...] mme_del | [...] meid_map | end | [| The on the end record indicates the number of mme_ar and mme_del records which were sent; if the count does not match the whole map is refused and dropped. The is the endpoint which should receive the message when a message is routed based on the MEID it contains. A MEID may be "owned" by only one endpoint, and if supplied multiple times, the last observed relationship is used. Each of the lists of MEIDs are blank separated. The optional on the *end* record should be the computed MD5 hash for all records which appear between the start and and records. This allows for a tighter verification that all data was received exactly as the route manager transmitted them. Environment ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To enable configuration of the library behaviour outside of direct user application control, RMr supports a number of environment variables which provide information to the library. The following is a list of the various environment variables, what they control and the defaults which RMr uses if undefined. RMR_ASYNC_CONN Allows the asynch connection mode to be turned off (by setting the value to 0. When set to 1, or missing from the environment, RMR will invoke the connection interface in the transport mechanism using the non-blocking (asynch) mode. This will likely result in many "soft failures" (retry) until the connection is established, but allows the application to continue unimpeeded should the connection be slow to set up. RMR_BIND_IF This provides the interface that RMr will bind listen ports to allowing for a single interface to be used rather than listening across all interfaces. This should be the IP address assigned to the interface that RMr should listen on, and if not defined RMr will listen on all interfaces. RMR_RTG_SVC RMr opens a TCP listen socket using the port defined by this environment variable and expects that the route table generator process will connect to this port. If not supplied the port 4561 is used. RMR_RTG_ISRAW Is set to 1 if the route table generator is sending "plain" messages (not using RMr to send messages, 0 if the rtg is using RMr to send. The default is 1 as we don't expect the rtg to use RMr. RMR_SEED_RT This is used to supply a static route table which can be used for debugging, testing, or if no route table generator process is being used to supply the route table. If not defined, no static table is used and RMr will not report *ready* until a table is received. The static route table may contain both the route table (between newrt start and end records), and the MEID map (between meid_map start and end records) RMR_SRC_ID This is either the name or IP address which is placed into outbound messages as the message source. This will used when an RMR based application uses the rmr_rts_msg() function to return a response to the sender. If not supplied RMR will use the hostname which in some container environments might not be routable. RMR_VCTL_FILE This supplies the name of a verbosity control file. The core RMR functions do not produce messages unless there is a critical failure. However, the route table collection thread, not a part of the main message processing component, can write additional messages to standard error. If this variable is set, RMR will extract the verbosity level for these messages (0 is silent) from the first line of the file. Changes to the file are detected and thus the level can be changed dynamically, however RMR will only suss out this variable during initialisation, so it is impossible to enable verbosity after startup. RMR_WARNINGS If set to 1, RMR will write some warnings which are non-performance impacting. If the variable is not defined, or set to 0, RMR will not write these additional warnings. SEE ALSO -------------------------------------------------------------------------------------------- rmr_alloc_msg(3), rmr_tralloc_msg(3), rmr_call(3), rmr_free_msg(3), rmr_init(3), rmr_init_trace(3), rmr_get_meid(3), rmr_get_src(3), rmr_get_srcip(3), rmr_get_trace(3), rmr_get_trlen(3), rmr_get_xact(3), rmr_payload_size(3), rmr_rcv_msg(3), rmr_rcv_specific(3), rmr_rts_msg(3), rmr_ready(3), rmr_fib(3), rmr_has_str(3), rmr_tokenise(3), rmr_mk_ring(3), rmr_realloc_payload(3), rmr_ring_free(3), rmr_set_trace(3), rmr_torcv_msg(3), rmr_wh_open(3), rmr_wh_send_msg(3)