208 lines
7.9 KiB
Markdown
208 lines
7.9 KiB
Markdown
This is a summary todo covering several subprojects, which would extend
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git-annex to be able to use proxies which sit in front of a cluster of
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repositories.
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1. [[design/passthrough_proxy]]
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2. [[design/p2p_protocol_over_http]]
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3. [[design/balanced_preferred_content]]
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4. [[todo/track_free_space_in_repos_via_git-annex_branch]]
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5. [[todo/proving_preferred_content_behavior]]
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## table of contents
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[[!toc ]]
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## planned schedule
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Joey has received funding to work on this.
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Planned schedule of work:
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* June: git-annex proxies and clusters
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* July, part 1: p2p protocol over http
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* July, part 2: git-annex proxy support for exporttree
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* August: balanced preferred content
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* September: streaming through proxy to special remotes (especially S3)
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* October: proving behavior of balanced preferred content with proxies
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[[!tag projects/openneuro]]
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## work notes
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* An interrupted PUT to cluster that has a node that is a special remote
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over http leaves open the connection to the cluster, so the next request
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opens another one.
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So does an interrupted PUT directly to the proxied ;
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special remote over http.
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* When part of a file has been sent to a cluster via the http server,
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the transfer interrupted, and another node is added to the cluster,
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and the transfer of the file performed again, there is a failure
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sending to the node that had an incomplete copy. It fails like this:
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//home/joey/tmp/bench/c3/.git/annex/tmp/SHA256E-s1048576000--09d7e19983a65682138fa5944f135e4fc593330c2693c41d22cc7881443d6060: withBinaryFile: illegal operation
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git-annex: transfer already in progress, or unable to take transfer lock
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p2pstdio: 1 failed
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When using ssh and not the http server, the node that had the incomplete
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copy also doesn't get the file, altough no error is displayed.
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* When proxying a PUT to a special remote, no verification of the received
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content is done, it's just written to a file and that is sent to the
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special remote. This violates a usual invariant that any data being
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received into a repository gets verified in passing. Although on the
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other hand, when sending data to a special remote normally, there is also
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no verification.
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## items deferred until later for p2p protocol over http
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* Support proxying to git remotes that use annex+http urls.
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* `git-annex p2phttp` could support systemd socket activation. This would
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allow making a systemd unit that listens on port 80.
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## completed items for July's work on p2p protocol over http
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* HTTP P2P protocol design [[design/p2p_protocol_over_http]].
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* addressed [[doc/todo/P2P_locking_connection_drop_safety]]
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* implemented server and client for HTTP P2P protocol
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* added git-annex p2phttp command to serve HTTP P2P protocol
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* Make git-annex p2phttp support https.
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* Allow using annex+http urls in remote.name.annexUrl
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* Make http server support proxying.
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* Make http server support serving a cluster.
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## items deferred until later for [[design/passthrough_proxy]]
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* Check annex.diskreserve when proxying for special remotes
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to avoid the proxy's disk filling up with the temporary object file
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cached there.
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* Resuming an interrupted download from proxied special remote makes the proxy
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re-download the whole content. It could instead keep some of the
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object files around when the client does not send SUCCESS. This would
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use more disk, but without streaming, proxying a special remote already
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needs some disk. And it could minimize to eg, the last 2 or so.
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The design doc has some more thoughts about this.
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* Streaming download from proxied special remotes. See design.
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(Planned for September)
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* When an upload to a cluster is distributed to multiple special remotes,
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a temporary file is written for each one, which may even happen in
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parallel. This is a lot of extra work and may use excess disk space.
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It should be possible to only write a single temp file.
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(With streaming this won't be an issue.)
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* Indirect uploads when proxying for special remote
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(to be considered). See design.
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* Getting a key from a cluster currently picks from amoung
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the lowest cost remotes at random. This could be smarter,
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eg prefer to avoid using remotes that are doing other transfers at the
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same time.
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* The cost of a proxied node that is accessed via an intermediate gateway
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is currently the same as a node accessed via the cluster gateway.
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To fix this, there needs to be some way to tell how many hops through
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gateways it takes to get to a node. Currently the only way is to
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guess based on number of dashes in the node name, which is not satisfying.
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Even counting hops is not very satisfying, one cluster gateway could
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be much more expensive to traverse than another one.
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If seriously tackling this, it might be worth making enough information
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available to use spanning tree protocol for routing inside clusters.
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* Optimise proxy speed. See design for ideas.
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* Speed: A proxy to a local git repository spawns git-annex-shell
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to communicate with it. It would be more efficient to operate
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directly on the Remote. Especially when transferring content to/from it.
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But: When a cluster has several nodes that are local git repositories,
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and is sending data to all of them, this would need an alternate
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interface than `storeKey`, which supports streaming, of chunks
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of a ByteString.
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* Use `sendfile()` to avoid data copying overhead when
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`receiveBytes` is being fed right into `sendBytes`.
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Library to use:
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<https://hackage.haskell.org/package/hsyscall-0.4/docs/System-Syscall.html>
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* Support using a proxy when its url is a P2P address.
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(Eg tor-annex remotes.)
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## completed items for June's work on [[design/passthrough_proxy]]:
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* UUID discovery via git-annex branch. Add a log file listing UUIDs
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accessible via proxy UUIDs. It also will contain the names
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of the remotes that the proxy is a proxy for,
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from the perspective of the proxy. (done)
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* Add `git-annex updateproxy` command (done)
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* Remote instantiation for proxies. (done)
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* Implement git-annex-shell proxying to git remotes. (done)
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* Proxy should update location tracking information for proxied remotes,
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so it is available to other users who sync with it. (done)
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* Implement `git-annex initcluster` and `git-annex updatecluster` commands (done)
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* Implement cluster UUID insertation on location log load, and removal
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on location log store. (done)
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* Omit cluster UUIDs when constructing drop proofs, since lockcontent will
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always fail on a cluster. (done)
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* Don't count cluster UUID as a copy in numcopies checking etc. (done)
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* Tab complete proxied remotes and clusters in eg --from option. (done)
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* Getting a key from a cluster should proxy from one of the nodes that has
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it. (done)
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* Implement upload with fanout to multiple cluster nodes and reporting back
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additional UUIDs over P2P protocol. (done)
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* Implement cluster drops, trying to remove from all nodes, and returning
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which UUIDs it was dropped from. (done)
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* `git-annex testremote` works against proxied remote and cluster. (done)
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* Avoid `git-annex sync --content` etc from operating on cluster nodes by
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default since syncing with a cluster implicitly syncs with its nodes. (done)
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* On upload to cluster, send to nodes where its preferred content, and not
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to other nodes. (done)
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* Support annex.jobs for clusters. (done)
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* Add `git-annex extendcluster` command and extend `git-annex updatecluster`
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to support clusters with multiple gateways. (done)
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* Support proxying for a remote that is proxied by another gateway of
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a cluster. (done)
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* Support distributed clusters: Make a proxy for a cluster repeat
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protocol messages on to any remotes that have the same UUID as
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the cluster. Needs extension to P2P protocol to avoid cycles.
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(done)
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* Proxied cluster nodes should have slightly higher cost than the cluster
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gateway. (done)
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* Basic support for proxying special remotes. (But not exporttree=yes ones
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yet.) (done)
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* Tab complete remotes in all relevant commands (done)
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* Display cluster and proxy information in git-annex info (done)
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