The remote_build Tool

05/15/2018 ∙ by Christian Sternagel, et al. ∙ Leopold Franzens Universität Innsbruck 0

This is an introduction to the remote_build tool for transparent remote session builds. The intended workflow for a user is to locally issue a build command for some session heap images and then continue working, while the actual build runs on a remote machine and the resulting heap images are synchronized incrementally as soon as they are available.

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0.1 Introduction

Many Isabelle users are familiar with the following scenario once their formal developments reach a certain size:

You make a change high up in the theory hierarchy but then want to continue with your latest theory that is a leaf of the hierarchy. So you initiate a build of an Isabelle session that covers all imports of your current theory and …take a break, since all the CPU cycles and gigabytes of RAM your computer has to offer are needed to finish the build within the next few hours and you will not even be able to read emails on the same machine in the meantime.

While the above might be slightly exaggerated, it is not that far from the truth. For example, building IsaFoR/CeTA 111http://cl-informatik.uibk.ac.at/isafor takes almost four hours on my current machine if only a single process is available, and requires at least 16 GB of RAM to succeed at all.

This is in contrast to only around one hour build time on a workstation with 12 processes available. Thus the obvious solution is that you build session heap images not on your local machine but instead on some decent remote machine. Often, you will still want to continue work on your local machine once the build is finished. So you have to copy the remotely built heap images to your local machine in such a way that Isabelle does not initiate a new build.

It is surely possible to do all this by hand, but it tends to get tedious after the th repetition. Which is why I introduce the Isabelle add-on tool remote_build, enabling transparent remote session builds. The intended workflow for a user is to locally issue a build command for some session heap images and then immediately continue work without the performance loss that often comes with time and computation intensive Isabelle builds. Meanwhile, the actual build is started on another machine and the resulting heap images are synchronized incrementally as soon as they are available.

0.2 Invoking the Build Process

The remote_build tool is implemented in Isabelle/Scala222http://isabelle.in.tum.de/doc/system.pdf (Chapter 4) and comes with a command line interface. Its usage is:

Usage: isabelle remote_build [OPTIONS] SESSIONS ...
  Options are:
    -B DIR       base directory for remote Isabelle installations (default:
                 $REMOTE_BUILD_REMOTE_BASE, or if former not set ~)
    -d DIR       include session directory
    -r HOST      remote host name (default: $REMOTE_BUILD_REMOTE_HOST)
    -o OPTION    add option for remote isabelle call, e.g., -o -d -o '$ISAFOR'
    -i           incremental: only synchronize heap images that are newly
                 built on the remote host (default: synchronize all session
                 heaps together with their ancestors)
    -P PROXY     connect to remote host via proxy jump; PROXY may either be a
                 HOST or a specification HOST:PORT (default PORT: 2222)
    -v           be verbose
  Build and copy heap images, observing implicit settings:
  REMOTE_BUILD_REMOTE_HOST="..."
  REMOTE_BUILD_REMOTE_BASE="..."

In order for remote_build to work properly, we need (at least) two computers, a local machine and a remote machine , with Isabelle installed. The respective installations should be reasonably similar (meaning if one of them is x86_64-linux, the other should be too; and of course the Isabelle versions should coincide). Also, the sessions you want to build and corresponding theory sources have to be present on both machines (for IsaFoR, I achieve this for example by using two clones of its mercurial repository, one on and one on ). Moreover, communication between and runs through SSH and the rsync333https://rsync.samba.org/ utility is used for heap image synchronization.

By default, the Isabelle installation on is expected to be located in the user home directory. This can be overwritten by explicitly setting the remote base directory with -B, or made persistent in by setting REMOTE_BUILD_REMOTE_BASE.

As for the standard build tool of Isabelle, (local) session directories can be specified via -d. Usually, this has to be reflected on the remote side. A general way of passing options to the Isabelle process invoked on is by -o (which takes a single word, no spaces, as argument).

The hostname/IP address of can be set explicitly using -r or made persistent by setting REMOTE_BUILD_REMOTE_HOST.

If -i is set, then remote_build enters incremental mode and only synchronizes heap images that are generated during the current build. This might occasionally be useful to save some time (for example, you might already have started to manually copy heap images from that existed before the build was initiated). The default behavior is to synchronize all ancestors of the built sessions.

If is not directly available via SSH, a proxy can be specified using -P, which works as long as is reachable via SSH from and is reachable via SSH from .

Usage examples.

This is, for example, how I build the whole of IsaFoR/CeTA from my office (“remote host” and “remote base” are implicit in my local settings):

isabelle remote_build -d'$ISAFOR' -o-d'$ISAFOR' CeTA

If I want to do the same from at home, I have to provide a proxy, since the “build machine” of our research group is not directly available from the outside:

isabelle remote_build -P proxy.uibk.ac.at -d'$ISAFOR' -o-d'$ISAFOR' CeTA

0.3 Installation Instructions

The remote_build tool is part of the IsaFoR/CeTA project since version 2.32 and compatible with Isabelle2017. Its sources reside in src/remote_build.scala.

Once you obtained the sources, the following steps are required to make remote_build locally available as Isabelle tool. Start by compiling the sources

isabelle scalac remote_build.scala

which should create the two files: Remote_Build.class and Remote_Build. Then, assemble a JAR archive remote_build.jar via:

jar cevf Remote_Build remote_build.jar \
                                Remote_Build.class 'Remote_Build$.class'

Now, say in a directory tools/, create the tool wrapper remote_build with content

#!/usr/bin/env bash
$ISABELLE_TOOL scala /path/to/remote_build.jar "$@"

and register it as Isabelle tool by adding

ISABELLE_TOOLS="$ISABELLE_TOOLS:/path/to/tools/"

to $ISABELLE_HOME_USER/etc/settings.

0.4 Some Further Details and Troubleshooting

The remote_build tool employs the available Isabelle/Scala interface to the JSch444http://www.jcraft.com/jsch/ Java implementation of the SSH2 protocol. Since the available interface does not cater for password authentication (which would be cumbersome anyway), the involved SSH connections assume key-based authentication. However, the current version does not seem to support ECDSA based host keys.555The only kind of keys I actually tested is RSA. Therefore, it will sometimes be necessary to set up an RSA host key.

To find out what kind of keys are currently known for a given host host, use

ssh-keygen -F host

which looks up host keys in ~/.ssh/known_hosts. To obtain an RSA key for host, use:

ssh-keyscan -t rsa host

Its output can directly be appended to the list of known hosts as follows:

ssh-keyscan -t rsa host >> ~/.ssh/known_hosts

In case a proxy is used between and , remote_build establishes, behind the scenes, the following SSH connections. First a connection from to with port-forwarding from to the SSH daemon of . That is, akin to:

ssh -L 2222:R:22 P

And in addition the actual connection between and that is carried inside the above port-forwarding channel. Which you could establish on a command line via ssh -p 2222 localhost. This setup, causes the peculiarity that an entry for [localhost]:2222 is needed in ~/.ssh/known_hosts that provides an RSA key for the remote host (so, if you change your remote host, also the key for [localhost]:2222 has to change, even though the hostname of the entry did not).