git-annex/doc/todo/git-annex_proxies.mdwn

273 lines
11 KiB
Text
Raw Normal View History

This is a summary todo covering several subprojects, which would extend
git-annex to be able to use proxies which sit in front of a cluster of
repositories.
2024-05-01 16:19:12 +00:00
1. [[design/passthrough_proxy]]
2. [[design/p2p_protocol_over_http]]
3. [[design/balanced_preferred_content]]
4. [[todo/track_free_space_in_repos_via_git-annex_branch]]
5. [[todo/proving_preferred_content_behavior]]
2024-07-01 15:38:29 +00:00
## table of contents
[[!toc ]]
## planned schedule
Joey has received funding to work on this.
Planned schedule of work:
2024-06-27 19:28:10 +00:00
* June: git-annex proxies and clusters
* July: p2p protocol over http
* August, part 1: git-annex proxy support for exporttree
2024-08-30 15:14:45 +00:00
* August, part 2: balanced preferred content
* October: proving behavior of balanced preferred content with proxies
2024-09-03 15:52:54 +00:00
* September: streaming through proxy to special remotes (especially S3)
[[!tag projects/openneuro]]
2024-06-04 11:51:33 +00:00
2024-07-01 15:38:29 +00:00
## work notes
2024-06-04 11:51:33 +00:00
tried a blind alley on streaming special remote download via proxy This didn't work. In case I want to revisit, here's what I tried. diff --git a/Annex/Proxy.hs b/Annex/Proxy.hs index 48222872c1..e4e526d3dd 100644 --- a/Annex/Proxy.hs +++ b/Annex/Proxy.hs @@ -26,16 +26,21 @@ import Logs.UUID import Logs.Location import Utility.Tmp.Dir import Utility.Metered +import Utility.ThreadScheduler +import Utility.OpenFd import Git.Types import qualified Database.Export as Export import Control.Concurrent.STM import Control.Concurrent.Async +import Control.Concurrent.MVar import qualified Data.ByteString as B +import qualified Data.ByteString as BS import qualified Data.ByteString.Lazy as L import qualified System.FilePath.ByteString as P import qualified Data.Map as M import qualified Data.Set as S +import System.IO.Unsafe proxyRemoteSide :: ProtocolVersion -> Bypass -> Remote -> Annex RemoteSide proxyRemoteSide clientmaxversion bypass r @@ -240,21 +245,99 @@ proxySpecialRemote protoversion r ihdl ohdl owaitv oclosedv mexportdb = go writeVerifyChunk iv h b storetofile iv h (n - fromIntegral (B.length b)) bs - proxyget offset af k = withproxytmpfile k $ \tmpfile -> do + proxyget offset af k = withproxytmpfile k $ \tmpfile -> + let retrieve = tryNonAsync $ Remote.retrieveKeyFile r k af + (fromRawFilePath tmpfile) nullMeterUpdate vc + in case fromKey keySize k of + Just size | size > 0 -> do + cancelv <- liftIO newEmptyMVar + donev <- liftIO newEmptyMVar + streamer <- liftIO $ async $ + streamdata offset tmpfile size cancelv donev + retrieve >>= \case + Right _ -> liftIO $ do + putMVar donev () + wait streamer + Left err -> liftIO $ do + putMVar cancelv () + wait streamer + propagateerror err + _ -> retrieve >>= \case + Right _ -> liftIO $ senddata offset tmpfile + Left err -> liftIO $ propagateerror err + where -- Don't verify the content from the remote, -- because the client will do its own verification. - let vc = Remote.NoVerify - tryNonAsync (Remote.retrieveKeyFile r k af (fromRawFilePath tmpfile) nullMeterUpdate vc) >>= \case - Right _ -> liftIO $ senddata offset tmpfile - Left err -> liftIO $ propagateerror err + vc = Remote.NoVerify + streamdata (Offset offset) f size cancelv donev = do + sendlen offset size + waitforfile + x <- tryNonAsync $ do + fd <- openFdWithMode f ReadOnly Nothing defaultFileFlags + h <- fdToHandle fd + hSeek h AbsoluteSeek offset + senddata' h (getcontents size) + case x of + Left err -> do + throwM err + Right res -> return res + where + -- The file doesn't exist at the start. + -- Wait for some data to be written to it as well, + -- in case an empty file is first created and then + -- overwritten. When there is an offset, wait for + -- the file to get that large. Note that this is not used + -- when the size is 0. + waitforfile = tryNonAsync (fromIntegral <$> getFileSize f) >>= \case + Right sz | sz > 0 && sz >= offset -> return () + _ -> ifM (isEmptyMVar cancelv) + ( do + threadDelaySeconds (Seconds 1) + waitforfile + , do + return () + ) + + getcontents n h = unsafeInterleaveIO $ do + isdone <- isEmptyMVar donev <||> isEmptyMVar cancelv + c <- BS.hGet h defaultChunkSize + let n' = n - fromIntegral (BS.length c) + let c' = L.fromChunks [BS.take (fromIntegral n) c] + if BS.null c + then if isdone + then return mempty + else do + -- Wait for more data to be + -- written to the file. + threadDelaySeconds (Seconds 1) + getcontents n h + else if n' > 0 + then do + -- unsafeInterleaveIO causes + -- this to be deferred until + -- data is read from the lazy + -- ByteString. + cs <- getcontents n' h + return $ L.append c' cs + else return c' + senddata (Offset offset) f = do size <- fromIntegral <$> getFileSize f - let n = max 0 (size - offset) - sendmessage $ DATA (Len n) + sendlen offset size withBinaryFile (fromRawFilePath f) ReadMode $ \h -> do hSeek h AbsoluteSeek offset - sendbs =<< L.hGetContents h + senddata' h L.hGetContents + + senddata' h getcontents = do + sendbs =<< getcontents h -- Important to keep the handle open until -- the client responds. The bytestring -- could still be lazily streaming out to @@ -272,6 +355,11 @@ proxySpecialRemote protoversion r ihdl ohdl owaitv oclosedv mexportdb = go Just FAILURE -> return () Just _ -> giveup "protocol error" Nothing -> return () + + sendlen offset size = do + let n = max 0 (size - offset) + sendmessage $ DATA (Len n) + {- Check if this repository can proxy for a specified remote uuid, - and if so enable proxying for it. -}
2024-10-07 17:54:04 +00:00
* Currently working on streaming download via proxy from special remote.
* Tried implementing a background thread in the proxy that runs while
retrieving a file, to stream it out as it comes in. That failed because
reading from a file that the same process is writing to is prevented by
locking in haskell. (Could be gotten around by using FD rather than Handle,
but would need to read from the FD and use packCString to make a ByteString.)
But also, remotes using fileRetriever retrieve to the temp object file,
before it is renamed to the requested file. In the case of a proxy,
that is a different file, and so it won't see the file until it's all
been transferred and renamed.
* Could the P2P protocol be used as an alternate interface for a special
remote? Would avoid needing temp files when proxying for special remotes,
and would support resume from offset as well for special remotes for
which that makes sense.
2024-09-20 15:26:40 +00:00
2024-09-25 18:26:32 +00:00
## completed items for September's work on proving behavior of preferred content
2024-09-25 18:26:32 +00:00
* Static analysis to detect "not present", "not balanced", and similar
unstable preferred content expressions and avoid problems with them.
* Implemented `git-annex sim` command.
* Simulated a variety of repository networks, and random preferred content
expressions, checking that a stable state is always reached.
* Fix bug that prevented anything being stored in an empty
repository whose preferred content expression uses sizebalanced.
(Identified via `git-annex sim`)
2024-08-30 15:14:45 +00:00
## items deferred until later for balanced preferred content and maxsize tracking
* The assistant is using NoLiveUpdate, but it should be posssible to plumb
a LiveUpdate through it from preferred content checking to location log
updating.
* `git-annex info` in the limitedcalc path in cachedAllRepoData
double-counts redundant information from the journal due to using
2024-08-28 15:00:59 +00:00
overLocationLogs. In the other path it does not (any more; it used to),
and this should be fixed for consistency and correctness.
* getLiveRepoSizes has a filterM getRecentChange over the live updates.
This could be optimised to a single sql join. There are usually not many
live updates, but sometimes there will be a great many recent changes,
2024-08-30 15:14:45 +00:00
so it might be worth doing this optimisation. Persistent is not capable
of this, would need dependency added on esquelito.
## completed items for August's work on balanced preferred content
* Balanced preferred content basic implementation, including --rebalance
option.
* Implemented [[track_free_space_in_repos_via_git-annex_branch]]
* Implemented tracking of live changes to repository sizes.
2024-08-22 11:53:56 +00:00
* `git-annex maxsize`
* annex.fullybalancedthreshhold
2024-08-08 19:34:36 +00:00
## completed items for August's work on git-annex proxy support for exporttre
2024-08-07 15:49:53 +00:00
* Special remotes configured with exporttree=yes annexobjects=yes
can store objects in .git/annex/objects, as well as an exported tree.
* Support proxying to special remotes configured with
exporttree=yes annexobjects=yes.
* post-retrieve: When proxying is enabled for an exporttree=yes
special remote and the configured remote.name.annex-tracking-branch
is received, the tree is exported to the special remote.
* When getting from a P2P HTTP remote, prompt for credentials when
required, instead of failing.
* Prevent `updateproxy` and `updatecluster` from adding
an exporttree=yes special remote that does not have
annexobjects=yes, to avoid foot shooting.
2024-08-08 18:05:05 +00:00
* Implement `git-annex export treeish --to=foo --from=bar`, which
gets from bar as needed to send to foo. Make post-retrieve use
`--to=r --from=r` to handle the multiple files case.
2024-07-28 18:22:44 +00:00
## items deferred until later for p2p protocol over http
2024-07-28 21:19:27 +00:00
* `git-annex p2phttp` should support serving several repositories at the same
time (not as proxied remotes), so that eg, every git-annex repository
on a server can be served on the same port.
2024-07-29 13:11:27 +00:00
* Support proxying to git remotes that use annex+http urls. This needs a
translation from P2P protocol to servant-client to P2P protocol.
* Should be possible to use a git-remote-annex annex::$uuid url as
remote.foo.url with remote.foo.annexUrl using annex+http, and so
not need a separate web server to serve the git repository. Doesn't work
currently because git-remote-annex urls only support special remotes.
It would need a new form of git-remote-annex url, eg:
annex::$uuid?annex+http://example.com/git-annex/
2024-07-28 18:22:44 +00:00
* `git-annex p2phttp` could support systemd socket activation. This would
allow making a systemd unit that listens on port 80.
2024-07-04 19:18:06 +00:00
## completed items for July's work on p2p protocol over http
2024-07-24 16:19:53 +00:00
* HTTP P2P protocol design [[design/p2p_protocol_over_http]].
2024-07-04 19:18:06 +00:00
2024-07-22 23:50:08 +00:00
* addressed [[doc/todo/P2P_locking_connection_drop_safety]]
2024-07-11 15:50:44 +00:00
* implemented server and client for HTTP P2P protocol
* added git-annex p2phttp command to serve HTTP P2P protocol
2024-07-23 19:37:36 +00:00
* Make git-annex p2phttp support https.
2024-07-24 16:19:53 +00:00
* Allow using annex+http urls in remote.name.annexUrl
2024-07-26 14:24:23 +00:00
* Make http server support proxying.
* Make http server support serving a cluster.
2024-07-02 20:16:37 +00:00
## items deferred until later for [[design/passthrough_proxy]]
2024-07-01 15:29:04 +00:00
* Check annex.diskreserve when proxying for special remotes
to avoid the proxy's disk filling up with the temporary object file
cached there.
* Resuming an interrupted download from proxied special remote makes the proxy
re-download the whole content. It could instead keep some of the
object files around when the client does not send SUCCESS. This would
use more disk, but without streaming, proxying a special remote already
needs some disk. And it could minimize to eg, the last 2 or so.
The design doc has some more thoughts about this.
* Streaming download from proxied special remotes. See design.
2024-07-01 15:29:04 +00:00
(Planned for September)
2024-06-27 16:57:08 +00:00
2024-07-01 15:33:07 +00:00
* When an upload to a cluster is distributed to multiple special remotes,
a temporary file is written for each one, which may even happen in
parallel. This is a lot of extra work and may use excess disk space.
It should be possible to only write a single temp file.
(With streaming this won't be an issue.)
2024-06-27 17:40:09 +00:00
* Indirect uploads when proxying for special remote
(to be considered). See design.
* Getting a key from a cluster currently picks from amoung
the lowest cost remotes at random. This could be smarter,
eg prefer to avoid using remotes that are doing other transfers at the
same time.
* The cost of a proxied node that is accessed via an intermediate gateway
is currently the same as a node accessed via the cluster gateway.
To fix this, there needs to be some way to tell how many hops through
gateways it takes to get to a node. Currently the only way is to
guess based on number of dashes in the node name, which is not satisfying.
Even counting hops is not very satisfying, one cluster gateway could
be much more expensive to traverse than another one.
If seriously tackling this, it might be worth making enough information
available to use spanning tree protocol for routing inside clusters.
2024-06-25 21:50:22 +00:00
2024-06-12 15:55:18 +00:00
* Optimise proxy speed. See design for ideas.
2024-06-04 11:51:33 +00:00
* Speed: A proxy to a local git repository spawns git-annex-shell
to communicate with it. It would be more efficient to operate
directly on the Remote. Especially when transferring content to/from it.
But: When a cluster has several nodes that are local git repositories,
and is sending data to all of them, this would need an alternate
interface than `storeKey`, which supports streaming, of chunks
of a ByteString.
2024-06-12 15:55:18 +00:00
* Use `sendfile()` to avoid data copying overhead when
`receiveBytes` is being fed right into `sendBytes`.
2024-06-25 21:26:26 +00:00
Library to use:
<https://hackage.haskell.org/package/hsyscall-0.4/docs/System-Syscall.html>
2024-06-04 11:51:33 +00:00
2024-06-12 15:55:18 +00:00
* Support using a proxy when its url is a P2P address.
(Eg tor-annex remotes.)
2024-06-23 16:31:00 +00:00
2024-07-01 15:38:29 +00:00
## completed items for June's work on [[design/passthrough_proxy]]:
2024-06-23 20:38:01 +00:00
* UUID discovery via git-annex branch. Add a log file listing UUIDs
accessible via proxy UUIDs. It also will contain the names
of the remotes that the proxy is a proxy for,
from the perspective of the proxy. (done)
* Add `git-annex updateproxy` command (done)
* Remote instantiation for proxies. (done)
* Implement git-annex-shell proxying to git remotes. (done)
* Proxy should update location tracking information for proxied remotes,
so it is available to other users who sync with it. (done)
2024-06-27 19:28:10 +00:00
* Implement `git-annex initcluster` and `git-annex updatecluster` commands (done)
2024-06-23 20:38:01 +00:00
* Implement cluster UUID insertation on location log load, and removal
on location log store. (done)
* Omit cluster UUIDs when constructing drop proofs, since lockcontent will
always fail on a cluster. (done)
* Don't count cluster UUID as a copy in numcopies checking etc. (done)
* Tab complete proxied remotes and clusters in eg --from option. (done)
* Getting a key from a cluster should proxy from one of the nodes that has
it. (done)
* Implement upload with fanout to multiple cluster nodes and reporting back
additional UUIDs over P2P protocol. (done)
* Implement cluster drops, trying to remove from all nodes, and returning
which UUIDs it was dropped from. (done)
* `git-annex testremote` works against proxied remote and cluster. (done)
don't sync with cluster nodes by default Avoid `git-annex sync --content` etc from operating on cluster nodes by default since syncing with a cluster implicitly syncs with its nodes. This avoids a lot of unncessary work when a cluster has a lot of nodes just in checking if each node's preferred content is satisfied. And it avoids content being sent to nodes individually, so instead syncing with clusters always fanout uploads to nodes. The downside is that there are situations where a cluster's preferred content settings can be met, but those of its nodes are not. Or where a node does not contain a key, but the cluster does, and there are not enough copies of the key yet, so it would be desirable the send it there. I think that's an acceptable tradeoff. These kind of situations are ones where the cluster itself should probably be responsible for copying content to the node. Which it can do much less expensively than a client can. Part of the balanced preferred content design that I will be working on in a couple of months involves rebalancing clusters, so I expect to revisit this. The use of annex-sync config does allow running git-annex sync with a specific node, or nodes, and it will sync with it. And it's also possible to set annex-sync git configs to make it sync with a node by default. (Although that will require setting up an explicit git remote for the node rather than relying on the proxied remote.) Logs.Cluster.Basic is needed because Remote.Git cannot import Logs.Cluster due to a cycle. And the Annex.Startup load of clusters happens too late for Remote.Git to use that. This does mean one redundant load of the cluster log, though only when there is a proxy.
2024-06-25 14:06:28 +00:00
* Avoid `git-annex sync --content` etc from operating on cluster nodes by
default since syncing with a cluster implicitly syncs with its nodes. (done)
* On upload to cluster, send to nodes where its preferred content, and not
to other nodes. (done)
2024-06-25 18:52:47 +00:00
* Support annex.jobs for clusters. (done)
* Add `git-annex extendcluster` command and extend `git-annex updatecluster`
to support clusters with multiple gateways. (done)
* Support proxying for a remote that is proxied by another gateway of
a cluster. (done)
* Support distributed clusters: Make a proxy for a cluster repeat
protocol messages on to any remotes that have the same UUID as
the cluster. Needs extension to P2P protocol to avoid cycles.
(done)
* Proxied cluster nodes should have slightly higher cost than the cluster
gateway. (done)
* Basic support for proxying special remotes. (But not exporttree=yes ones
yet.) (done)
2024-07-01 15:29:04 +00:00
* Tab complete remotes in all relevant commands (done)
* Display cluster and proxy information in git-annex info (done)