commit 3d6232cfa097f9e9102aaeb423472ef486dad730 Author: Mike Perry mikeperry-git@fscked.org Date: Mon Oct 1 14:38:54 2012 -0700
Add proposal for consensus bootstrapping. --- .../xxx-faster-headless-consensus-bootstrap.txt | 78 ++++++++++++++++++++ 1 files changed, 78 insertions(+), 0 deletions(-)
diff --git a/proposals/xxx-faster-headless-consensus-bootstrap.txt b/proposals/xxx-faster-headless-consensus-bootstrap.txt new file mode 100644 index 0000000..2fd34c1 --- /dev/null +++ b/proposals/xxx-faster-headless-consensus-bootstrap.txt @@ -0,0 +1,78 @@ +Title: Faster Headless Consensus Bootstrapping +Author: Mike Perry +Created: 01-10-2012 +Status: Open +Target: 0.2.4.x+ + + +Overview + + This proposal describes a way for clients to fetch the initial consensus + more quickly in situations where some or all of the directory authorities + are unreachable. It is meant to describe a solution for Bug #4483. + +Description + + The core idea is to attempt to establish bootstrap connections in + parallel during the bootstrap process, and download the consensus from the + first connection that completes. + + Connection attempts will be done in batches of five. Only one connection + will be performed to one of the canonical directory authorities. Four + connections will be performed to randomly chosen hard coded directory + mirrors. + + If no connections complete within 5 seconds, another batch of five + connections will be launched. Otherwise, the first connection to complete + will be used to download the consensus document, after which + bootstrapping will proceed as normal. + + If at any time, the total open bootstrap connection attempts exceeds + 25, no new connection attempts are to be launched until existing + connection attempts experience full timeout. + +Fallback Dir Mirror Selection + + The set of hard coded directory mirrors from #572 shall be chosen using + the 50 Guard nodes with the longest uptime. + + The fallback weights will be set using each mirror's fraction of + consensus bandwidth out of the total of all 50 mirrors. + + This list of fallback dir mirrors should be updated with every + major Tor release. + +Implementation Notes + + The implementation of the bootstrap process is unfortunately mixed + in with many types of directory activity. + + The process starts in update_consensus_networkstatus_downloads(), + which initiates a single directory connection through + directory_get_from_dirserver(). Depending on bootstrap state, + a single directory server is selected and a connection is + eventually made through directory_initiate_command_rend(). + + There appear to be a few options for altering this code to perform + multiple connections. Without refactoring, one approach would be + to make multiple calls to directory_initiate_command_routerstatus() + from directory_get_from_dirserver() if the purpose is + DIR_PURPOSE_FETCH_CONSENSUS and the only directory servers available + are the authorities and the fallback dir mirrors. + + The code in directory_initiate_command_rend() would then + need to be altered to maintain a list of the dircons created for this + purpose as well as avoid immediately queuing the directory_send_command() + request for the DIR_PURPOSE_FETCH_CONSENSUS purpose. A flag would need to + be set on the dircon to be checked in connection_dir_finished_connecting(). + + The function connection_dir_finished_connecting() would need to be altered to + examine the list of pending dircons, determine if this one is the first to + complete, and if so, then call directory_send_command() to download the + consensus and close the other pending dircons. + + An additional timer would need to be installed to re-call + update_consensus_networkstatus_downloads() or a related helper after 5 + seconds. connection_dir_finished_connecting() would cancel this timer. + The helper would check the list of pending connections and ensure it + never exceeds 25.