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This tool uses the RRDP data from a (single) "hidden" backend RPKI Publication Server to make a consistent local copy of that data.

This is intended to facilitate a redundant set up where one or more public https and rsync servers are used to make the RPKI repository content available.


29-11-2022 v0.2.1

This release includes fixes for the following issues:

  • Support empty snapshot (#62)
  • Increase cleanup-after default to 1 hour (#54)
  • Write new notification file only on change (#55)
  • Respect --insecure option (#59)

13-12-2021 v0.2.0

The code has had a massive overhaul since version 0.1.x. It has been simplified and has much better test coverage.

Functionality should be compatible to the known requirements for 0.1.x - but the CLI arguments have also changed. If you are looking to upgrade from 0.1.x to this version, please make sure that you read the updated text below and test things thoroughly. In case you run into any issues, do not hesitate to contact us or make an issue in GitHub.

29-04-2021 v0.1.3

In this version we added the following:

  • Allow a configurable delay before writing the RRDP notification.xml file (#5)
  • Use a symlink for the current rsync directory (#2)
  • Debian packages (#11)
  • Docker file (#9)

We did not make official releases, nor dir we keep any changelogs for earlier versions.


Install using Pre-built Packages

Assuming you have a machine running a recent Debian or Ubuntu distribution, you can install krill-sync from our software package repository. To use this repository, add the line below that corresponds to your operating system to your /etc/apt/sources.list or /etc/apt/sources.list.d/

deb [arch=amd64] stretch main
deb [arch=amd64] buster main
deb [arch=amd64] bullseye main
deb [arch=amd64] xenial main
deb [arch=amd64] bionic main
deb [arch=amd64] focal main

Then run the following commands.

wget -qO- | sudo apt-key add -
sudo apt update

You can then install krill-sync by running

sudo apt install krill-sync

Build with Cargo

For Ubuntu 20.04 with Rust 1.51.0:

apt update && apt install -y build-essential curl libssl-dev openssl pkg-config
curl --proto '=https' --tlsv1.2 -sSf | sh
source $HOME/.cargo/env
cargo install --git --tag v0.2.0-rc1 --locked


This tool is intended to enable public facing RRDP and Rsync servers to serve consistent and fresh content obtained from a "hidden" RRDP source server, e.g. that runs an RPKI Publication Server. In this context "hidden" means that the server is not reachable by the public name of the repository but creates content that points to the public name.

Data Retrieval and Assumptions

The repository data is retrieved by using the RRDP protocol itself, pointed at a hidden back-end server. krill-sync (as of 0.2.x) assumes that the back-end publication server uses the intended public URIs for its RRDP files. But, importantly, we can instruct it to map the URI of a given public RRDP notification URI to an alternative hidden backend server:

krill-sync --source_uri_base https://hidden.server/rrdp/ https://some.server/rrdp/notification.xml

There is a further assumption that snapshot and delta file URIs will use the same hostname and base path as the notification file, so that it can be resolved to the back-end using the same --source_uri_base map that is used for the notification file itself.

Using the RRDP protocol as a source ensures that only complete and consistent data is downloaded by following the Notification File to the dependent resources (assuming a publication server such as Krill that ensures that the Notification File is written last during a content update). It also enables the public servers to download only deltas rather than the entire snapshot on update keeping the sync time, bandwidth usage and origin server impact to a minimum.

Other means of synchronizing the content (e.g. rsync, scp, or possibly even file system replication tools like GlusterFS) are not RRDP aware and thus may sync the Notification File before the files it references have all been downloaded which can cause Relying Party clients of the public facing repository servers to encounter errors while attempting to download updates from the service.


When krill-sync runs without previous state, it will retrieve and parse the specified notification file. Then it will retrieve and parse the snapshot file to obtain all current objects, as well as each delta file mentioned (unless an optional hard limit is set, see below).

If a file cannot be retrieved or parsed then the run will fail. This means that if the back-end system RFC 8182 RRDP XML is somehow not understood by krill-sync the data will not be accepted.

The tool will persist its current state to disk. The default directory for this is /var/lib/krill-sync but this can be overridden using the --state-dir argument.

On subsequent runs krill-sync will check whether delta files can be used to update its current state. I.e. the session is unchanged and there is a chain of delta files available. If not, it will re-sync using the current back-end snapshot.

We recommend that you run krill-sync at least every 5 minutes from cron, but every minute should be fine too. Make sure that errors are reported back to you, e.g. by having cron email them. Note that a krill-sync invocation will abort with an error message if it finds that another instance (previous invocation) is still running. In that case you may have to reduce the frequency. That said, we found that on reasonably fast hardware a clean krill-sync takes less than a minute even for huge repositories, and subsequent updates are even faster.

Produced RRDP Data

This tool produces its own RRDP data XML. This means that the formatting, hash values and even the URI paths of the RRDP files produced by this tool may be different from the back-end. This is not issue as long as all your public facing RRDP front-ends use krill-sync.

The RRDP files are written in a safe order, meaning: new snapshot and delta files are written to disk first. Then a new notification file is written to a temporary file, which is then renamed to avoid avoid race conditions resulting from overwriting this file as it's being served.

Old snapshot and delta files are marked as 'deprecated' as soon they are no longer referenced by the current notification file. Files which have been deprecated for longer than N seconds are removed at the end of each synchronization. The default is 600 seconds, or 10 minutes, but note that this can be configured, and that the clean up only happens when an actual synchronization is done.

The default base directory for these files is /var/lib/krill-sync/rrdp/, but this can be overridden using the --rrdp-dir argument. The notification file will be called notification.xml and will be published directly under this base directory. Snapshot files are called snapshot.xml, delta files delta.xml. Snapshot and delta files are stored under two further directories based on the session ID, which is a UUID, and the serial.

Example of a resulting structure:


Make sure that you map the base directory in your HTTPS front-end server, such as NGINX, to this base directory in a way that the given public RRDP notification URI will map to the file on disk.

Rsync Data

Directory content for serving by an Rsync daemon is also created from the data downloaded via RRDP, no rsync binary is needed. If you do not need to serve the rsync content on a specific machine, then you can suppress this by using the --disable-rsync option.

This tool writes complete new rsync directories for each new RRDP session and serial that is retrieved. On UNIX like systems symlinks are then used to link the current directory to the latest content. As it turns out the rsync daemon resolves symlinks whenever a client connects, so ongoing connections will keep being served the directory which was current at the time of connection.

The previous directory is marked as deprecated whenever a new current directory is created this way. At the end of each synchronization directories which have been deprecated for more than N seconds (default 10 mins) are removed.

By default the base directory for these rsync directories is /var/lib/krill-sync/rsync/, but this can be overridden using the --rsync-dir argument. Your rsyncd process should be configured to serve the current directory, e.g.:

$ cat /etc/rsyncd.conf
uid = nobody
gid = nogroup
max connections = 50
socket options = SO_KEEPALIVE

[repo] ## <-- Use your public rsync module name here!
path = /var/lib/krill-sync/rsync/current/
comment = RPKI repository
read only = yes

CLI Usage

This tool is intended to be used as a system "service" invoked periodically e.g. once a minute from cron, it is not meant to be a user facing tool. As such it follows Linux FHS guidelines for storing application state rather than user state.

krill-sync --help
krill-sync 0.2.0
A tool to synchronize an RRDP and/or Rsync server with a remote RRDP publication point.

    krill-sync [FLAGS] [OPTIONS] <notification-uri>

    -h, --help             Prints help information
        --insecure         Whether or not localhost connections and self-signed certificates are allowed
    -q, --quiet            Quiet mode (no warnings or informative messages, only errors)
        --rsync-disable    Disable writing the rsync files
    -V, --version          Prints version information
    -v, --verbose          Verbose mode (-v, -vv, -vvv, etc.)

        --cleanup-after <seconds>        Remove unreferenced files and directories older than X seconds [default: 600]
        --rrdp-dir <dir>                 The directory to write RRDP files to [default: /var/lib/krill-sync/rrdp]
        --rrdp-max-deltas <number>       Optional hard upper limit to the number of deltas
        --rrdp-notify-delay <seconds>    Delay seconds before writing the notification.xml file [default: 0]
        --rsync-dir <dir>                The directory to write Rsync files to [default: /var/lib/krill-sync/rsync]
        --source_uri_base <uri>          Base uri for the notify file on the back-end server. Must end with a slash
    -s, --state-dir <dir>                The directory to write state to [default: /var/lib/krill-sync]

    <notification-uri>    The public RRDP notification URI

Tip: If connecting directly to a Krill server, and not to e.g. NGINX in front of Krill, you will need to use --insecure as the Krill RRDP service uses a self-signed TLS certificate.

Log filtering

By default krill-sync will output only warnings and errors. Using -v or --verbose repeatedly will cause krill-sync to print more and more detailed information about its activity. The first three levels enable info, debug and trace logging for krill-sync itself. The three levels after that enable info, debug and trace logging for 3rd party Rust crates that krill-sync uses.


A tool to synchronize an RRDP and/or Rsync server with a "hidden" remote RFC 8182 RRDP publication point.







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