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git01.mediatek.com / haproxy / b26a6f97083138504abf3d61b1e0d698223a9dcb / . / doc / peers.txt
blob: f308f8c7e88f7054a233bc83f53345937b6920ee [file] [log] [blame]
Willy Tarreau99795b12017-11-24 18:10:24 +0100[diff] [blame]1 +--------------------+
2 | Peers protocol 2.1 |
3 +--------------------+
Frédéric Lécaille4b6645d2017-11-15 14:41:00 +0100[diff] [blame]4
5
6 Peers protocol has been implemented over TCP. Its aim is to transmit
7 stick-table entries information between several haproxy processes.
8
9 This protocol is symmetrical. This means that at any time, each peer
10 may connect to other peers they have been configured for, so that to send
11 their last stick-table updates. There is no role of client or server in this
12 protocol. As peers may connect to each others at the same time, the protocol
13 ensures that only one peer session may stay opened between a couple of peers
14 before they start sending their stick-table information, possibly in both
15 directions (or not).
16
17
18 Handshake
19 +++++++++
20
21 Just after having connected to another one, a peer must identified itself
22 and identify the remote peer, sending a "hello" message. The remote peer
23 replies with a "status" message.
24
25 A "hello" message is made of three lines terminated by a line feed character
26 as follows:
27
28 <protocol identifier> <version>\n
29 <remote peer identifier>\n
30 <local peer identifier> <process ID> <relative process ID>\n
31
32 protocol identifier : HAProxyS
33 version : 2.1
34 remote peer identifier: the peer name this "hello" message is sent to.
35 local peer identifier : the name of the peer which sends this "hello" message.
36 process ID : the ID of the process handling this peer session.
37 relative process ID : the haproxy's relative process ID (0 if nbproc == 1).
38
39 The "status" message is made of a unique line terminated by a line feed
40 character as follows:
41
42 <status code>\n
43
44 with these values as status code (a three-digit number):
45
46 +-------------+---------------------------------+
47 | status code | signification |
48 +-------------+---------------------------------+
49 | 200 | Handshake succeeded |
50 +-------------+---------------------------------+
51 | 300 | Try again later |
52 +-------------+---------------------------------+
53 | 501 | Protocol error |
54 +-------------+---------------------------------+
55 | 502 | Bad version |
56 +-------------+---------------------------------+
57 | 503 | Local peer identifier mismatch |
58 +-------------+---------------------------------+
59 | 504 | Remote peer identifier mismatch |
60 +-------------+---------------------------------+
61
62 As the protocol is symmetrical, some peers may connect to each others at the
63 same time. For efficiency reasons, the protocol ensures there may be only
64 one TCP session opened after the handshake succeeded and before transmitting
65 any stick-table data information. In fact for each couple of peer, this is
66 the last connected peer which wins. Each time a peer A receives a "hello"
67 message from a peer B, peer A checks if it already managed to open a peer
68 session with peer B, so with a successful handshake. If it is the case,
69 peer A closes its peer session. So, this is the peer session opened by B
70 which stays opened.
71
72
73 Peer A Peer B
74 hello
75 ---------------------->
76 status 200
77 <----------------------
78 hello
79 <++++++++++++++++++++++
80 TCP/FIN-ACK
81 ---------------------->
82 TCP/FIN-ACK
83 <----------------------
84 status 200
85 ++++++++++++++++++++++>
86 data
87 <++++++++++++++++++++++
88 data
89 ++++++++++++++++++++++>
90 data
91 ++++++++++++++++++++++>
92 data
93 <++++++++++++++++++++++
94 .
95 .
96 .
97
98 As it is still possible that a couple of peers decide to close both their
99 peer sessions at the same time, the protocol ensures peers will not reconnect
100 at the same time, adding a random delay (50 up to 2050 ms) before any
101 reconnection.
102
103
104 Encoding
105 ++++++++
106
107 As some TCP data may be corrupted, for integrity reason, some data fields
108 are encoded at peer session level.
109
110 The following algorithms explain how to encode/decode the data.
111
112 encode:
113 input : val (64bits integer)
114 output: bitf (variable-length bitfield)
115
116 if val has no bit set above bit 4 (or if val is less than 0xf0)
117 set the next byte of bitf to the value of val
118 return bitf
119
120 set the next byte of bitf to the value of val OR'ed with 0xf0
121 substract 0xf0 from val
122 right shift val by 4
123
124 while val bit 7 is set (or if val is greater or equal to 0x80):
125 set the next byte of bitf to the value of the byte made of the last
126 7 bits of val OR'ed with 0x80
127 substract 0x80 from val
128 right shift val by 7
129
130 set the next byte of bitf to the value of val
131 return bitf
132
133 decode:
134 input : bitf (variable-length bitfield)
135 output: val (64bits integer)
136
137 set val to the value of the first byte of bitf
138 if bit 4 up to 7 of val are not set
139 return val
140
141 set loop to 0
142 do
143 add to val the value of the next byte of bitf left shifted by (4 + 7*loop)
144 set loop to (loop + 1)
145 while the bit 7 of the next byte of bitf is set
146 return val
147
148 Example:
149
150 let's say that we must encode 0x1234.
151
152 "set the next byte of bitf to the value of val OR'ed with 0xf0"
153 => bitf[0] = (0x1234 | 0xf0) & 0xff = 0xf4
154
155 "substract 0xf0 from val"
156 => val = 0x1144
157
158 right shift val by 4
159 => val = 0x114
160
161 "set the next byte of bitf to the value of the byte made of the last
162 7 bits of val OR'ed with 0x80"
163 => bitf[1] = (0x114 | 0x80) & 0xff = 0x94
164
165 "substract 0x80 from val"
166 => val= 0x94
167
168 "right shift val by 7"
169 => val = 0x1
170
171 => bitf[2] = 0x1
172
173 So, the encoded value of 0x1234 is 0xf49401.
174
175 To decode this value:
176
177 "set val to the value of the first byte of bitf"
178 => val = 0xf4
179
180 "add to val the value of the next byte of bitf left shifted by 4"
181 => val = 0xf4 + (0x94 << 4) = 0xf4 + 0x940 = 0xa34
182
183 "add to val the value of the next byte of bitf left shifted by (4 + 7)"
184 => val = 0xa34 + (0x01 << 11) = 0xa34 + 0x800 = 0x1234
185
186
187 Messages
188 ++++++++
189
190 *** General ***
191
192 After the handshake has successfully completed, peers are authorized to send
193 some messages to each others, possibly in both direction.
194
195 All the messages are made at least of a two bytes length header.
196
197 The first byte of this header identifies the class of the message. The next
198 byte identifies the type of message in the class.
199
200 Some of these messages are variable-length. Others have a fixed size.
201 Variable-length messages are identified by the value of the message type
202 byte. For such messages, it is greater than or equal to 128.
203
204 All variable-length message headers must be followed by the encoded length
205 of the remaining bytes (so the encoded length of the message minus 2 bytes
206 for the header and minus the length of the encoded length).
207
208 There exist four classes of messages:
209
210 +------------+---------------------+--------------+
211 | class byte | signification | message size |
212 +------------+---------------------+--------------+
213 | 0 | control | fixed (2) |
214 +------------+---------------------+--------------|
215 | 1 | error | fixed (2) |
216 +------------+---------------------+--------------|
217 | 10 | stick-table updates | variable |
218 +------------+---------------------+--------------|
219 | 255 | reserved | |
220 +------------+---------------------+--------------+
221
222 At this time of this writing, only control and error messages have a fixed
223 size of two bytes (header only). The stick-table updates messages are all
224 variable-length (their message type bytes are greater than 128).
225
226
227 *** Control message class ***
228
229 At this time of writing, control messages are fixed-length messages used
230 only to control the synchonrizations between local and/or remote processes.
231
232 There exist four types of such control messages:
233
234 +------------+--------------------------------------------------------+
235 | type byte | signification |
236 +------------+--------------------------------------------------------+
237 | 0 | synchronisation request: ask a remote peer for a full |
238 | | synchronization |
239 +------------+--------------------------------------------------------+
240 | 1 | synchronization finished: signal a remote peer that |
241 | | local updates have been pushed and local is considered |
242 | | up to date. |
243 +------------+--------------------------------------------------------+
244 | 2 | synchronization partial: signal a remote peer that |
245 | | local updates have been pushed and local is not |
246 | | considered up to date. |
247 +------------+--------------------------------------------------------+
248 | 3 | synchronization confirmed: acknowledge a finished or |
249 | | partial synchronization message. |
250 +------------+--------------------------------------------------------+
251
252
253 *** Error message class ***
254
255 There exits two types of such error messages:
256
257 +-----------+------------------+
258 | type byte | signification |
259 +-----------+------------------+
260 | 0 | protocol error |
261 +-----------+------------------+
262 | 1 | size limit error |
263 +-----------+------------------+
264
265
266 *** Stick-table update message class ***
267
268 This class is the more important one because it is in relation with the
269 stick-table entries handling between peers which is at the core of peers
270 protocol.
271
272 All the messages of this class are variable-length. Their type bytes are
273 all greater than or equal to 128.
274
275 There exits five types of such stick-table update messages:
276
277 +-----------+--------------------------------+
278 | type byte | signification |
279 +-----------+--------------------------------+
280 | 128 | Entry update |
281 +-----------+--------------------------------+
282 | 129 | Incremental entry update |
283 +-----------+--------------------------------+
284 | 130 | Stick-table definition |
285 +-----------+--------------------------------+
286 | 131 | Stick-table switch (unused) |
287 +-----------+--------------------------------+
288 | 133 | Update message acknowledgement |
289 +-----------+--------------------------------+
290
291 Note that entry update messages may be multiplexed. This means that different
292 entry update messages for different stick-tables may be sent over the same
293 peer session.
294
295 To do so, each time entry update messages have to sent, they must be preceeded
296 by a stick-table definition message. This remains true for incremental entry
297 update messages.
298
299 As its name indicate, "Update message acknowledgement" messages are used to
300 acknowledge the entry update messages.
301
302 In this following paragraph, we give some information about the format of
303 each stick-table update messages. This very simple following legend will
304 contribute in understanding it. The unit used is the octet.
305
306 XX
307 +-----------+
308 | foo | Unique fixed sized "foo" field, made of XX octets.
309 +-----------+
310
311 +===========+
312 | foo | Variable-length "foo" field.
313 +===========+
314
315 +xxxxxxxxxxx+
316 | foo | Encoded variable-length "foo" field.
317 +xxxxxxxxxxx+
318
319 +###########+
320 | foo | hereunder described "foo" field.
321 +###########+
322
323
324 With this legend, all the stick-table update messages have such a header:
325
326 1 1
327 +--------------------+------------------------+xxxxxxxxxxxxxxxx+
328 | Message Class (10) | Message type (128-133) | Message length |
329 +--------------------+------------------------+xxxxxxxxxxxxxxxx+
330
331 Note that to help in making communicate different versions of peers protocol,
332 such stick-table update messages may be extended adding non mandatory
333 fields at the end of such messages, announcing a total message length
334 which is greater than the message length of the previous versions of
335 peers protocol. After having parsed such messages, the remaining ones
336 will be skipped to parse the next message.
337
338 - Definition message format:
339
340 Before sending entry update messages, a peer must announce the configuration
341 of the stick-table in relation with these messages thanks to a
342 "Stick-table definition" message with such a following format:
343
344 +xxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxx+==================+
345 | Stick-table ID | Stick-table name length | Stick-table name |
346 +xxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxx+==================+
347
348 +xxxxxxxxxxxx+xxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxx+
349 | Key type | Key length | Data types bitfield | Expiry |
350 +xxxxxxxxxxxx+xxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxx+
351
352 +xxxxxxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx+
353 | Frequency counter #1 | Frequency counter #1 period |
354 +xxxxxxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx+
355
356 +xxxxxxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx+
357 | Frequency counter #2 | Frequency counter #2 period |
358 +xxxxxxxxxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx+
359 .
360 .
361 .
362
363 Note that "Stick-table ID" field is an encoded integer which is used to
364 identify the stick-table without using its name (or "Stick-table name"
365 field). It is local to the process handling the stick-table. So we can have
366 two peers attached to processes which generate stick-table updates for
367 the same stick-table (same name) but with different stick-table IDs.
368
369 Also note that the list of "Frequency counter #X" and their associated
370 periods fields exists only if their underlying types are already defined
371 in "Data types bitfield" field.
372
373 "Expiry" field and the remaining ones are not used by all the existing
374 version of haproxy peers. But they are MANDATORY, so that to make a
375 stick-table aggregator peer be able to autoconfigure itself.
376
377
378 - Entry update message format:
379 4
380 +-----------------+###########+############+
381 | Local update ID | Key | Data |
382 +-----------------+###########+############+
383
384 with "Key" described as follows:
385
386 +xxxxxxxxxxx+=======+
387 | length | value | if key type is (non null terminated) "string",
388 +xxxxxxxxxxx+=======+
389
390 4
391 +-------+
392 | value | if key type is "integer",
393 +-------+
394
395 +=======+
396 | value | for other key types: the size is announced in
397 +=======+ the previous stick-table definition message.
398
399 "Data" field is basically a list of encoded values for each type announced
400 by the "Data types bitfield" field of the previous "Stick-table definition"
401 message:
402
403 +xxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxx+ +xxxxxxxxxxxxxxxxxxxx+
404 | Data type #1 value | Data type #2 value | .... | Data type #n value |
405 +xxxxxxxxxxxxxxxxxxxx+xxxxxxxxxxxxxxxxxxxx+ +xxxxxxxxxxxxxxxxxxxx+
406
407
408
409 - Update message acknowledgement format:
410
411 These messages are responses to "Entry update" messages only.
412
413 Its format is very basic for efficiency reasons:
414
415 4
416 +xxxxxxxxxxxxxxxx+-----------+
417 | Stick-table ID | Update ID |
418 +xxxxxxxxxxxxxxxx+-----------+
419
420
421 Note that the "Stick-table ID" field value is in relation with the one which
422 has been previously announce by a "Stick-table definition" message.
423
424 The following schema may help in understanding how to handle a stream of
425 stick-table update messages. The handshake step is not represented.
426 Stick-table IDs are preceded by a '#' character.
427
428
429 Peer A Peer B
430
431 stkt def. #1
432 ---------------------->
433 updates (1-5)
434 ---------------------->
435 stkt def. #3
436 ---------------------->
437 updates (1000-1005)
438 ---------------------->
439
440 stkt def. #2
441 <----------------------
442 updates (10-15)
443 <----------------------
444 ack 5 for #1
445 <----------------------
446 ack 1005 for #3
447 <----------------------
448 stkt def. #4
449 <----------------------
450 updates (100-105)
451 <----------------------
452
453 ack 10 for #2
454 ---------------------->
455 ack 105 for #4
456 ---------------------->
457 (from here, on both sides, all stick-table updates
458 are considered as received)
459