Internet DRAFT - draft-timbru-sidrops-publication-server-bcp
draft-timbru-sidrops-publication-server-bcp
Network Working Group T. Bruijnzeels
Internet-Draft T. de Kock
Obsoletes: 8416 (if approved) RIPE NCC
Intended status: Best Current Practice F. Hill
Expires: 21 July 2024 ARIN
T. Harrison
APNIC
18 January 2024
RPKI Publication Server Best Current Practices
draft-timbru-sidrops-publication-server-bcp-02
Abstract
This document describes best current practices for operating an RFC
8181 RPKI Publication Server and its rsync (RFC 5781) and RRDP (RFC
8182) public repositories.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 21 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Publication Server . . . . . . . . . . . . . . . . . . . . . 3
4.1. Availability . . . . . . . . . . . . . . . . . . . . . . 3
5. RRDP Repository . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Unique Hostname . . . . . . . . . . . . . . . . . . . . . 4
5.2. Bandwidth and Data Usage . . . . . . . . . . . . . . . . 4
5.2.1. Content Delivery Network . . . . . . . . . . . . . . 5
5.2.2. Limit Notification File Size . . . . . . . . . . . . 5
5.2.3. Manifest and CRL Update Times . . . . . . . . . . . . 6
5.3. Consistent load-balancing . . . . . . . . . . . . . . . . 6
5.3.1. Notification File Timing . . . . . . . . . . . . . . 6
5.3.2. L4 load-balancing . . . . . . . . . . . . . . . . . . 7
6. Rsync Repository . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Consistent Content . . . . . . . . . . . . . . . . . . . 8
6.2. Deterministic Timestamps . . . . . . . . . . . . . . . . 9
6.3. Load Balancing and Testing . . . . . . . . . . . . . . . 9
7. Single CA Repositories . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 10
10. Informative References . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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2. Introduction
[RFC8181] describes the RPKI Publication Protocol used between RPKI
Certificate Authorities (CAs) and their Publication Repository
server. The server is responsible for handling publication requests
sent by the CAs, called Publishers in this context, and ensuring that
their data is made available to RPKI Relying Parties (RPs) in
(public) rsync and RRDP [RFC8182] publication points.
In this document, we will describe best current practices based on
the operational experience of several implementers and operators.
3. Glossary
+====================+=========================================+
| Term | Description |
+====================+=========================================+
| Publication Server | [RFC8181] Publication Repository server |
+--------------------+-----------------------------------------+
| Publishers | [RFC8181] Publishers (Certificate |
| | Authorities) |
+--------------------+-----------------------------------------+
| RRDP Repository | Public facing [RFC8182] RRDP repository |
+--------------------+-----------------------------------------+
| Rsync Repository | Public facing rsync server |
+--------------------+-----------------------------------------+
Table 1
4. Publication Server
The Publication Server handles the server side of the [RFC8181]
Publication Protocol. The Publication Server generates the content
for the public-facing RRDP and Rsync Repositories. It is strongly
RECOMMENDED that these functions are separated from serving the
repository content.
4.1. Availability
The Publication Server and repository content have different demands
on their availability and reachability. While the repository content
MUST be highly available to any RP worldwide, only publishers need to
access the Publication Server. Dependent on the specific setup, this
may allow for additional access restrictions in this context. For
example, the Publication Server can limit access to known source IP
addresses or apply rate limits.
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If the Publication Server is unavailable for some reason, this will
prevent Publishers from publishing any updated RPKI objects. The
most immediate impact of this is that the publisher cannot update
their ROAs, ASPAs or BGPSec Router Certificates during this outage.
Thus, it cannot authorise changes in its routing operations. If the
outage persists for a more extended period, then the RPKI manifests
and CRLs published will expire, resulting in the RPs rejecting CA
publication points.
For this reason, the Publication Server MUST be operated in a highly
available fashion. Maintenance windows SHOULD be planned and
communicated to publishers, so they can avoid - if possible - that
changes in published RPKI objects are needed during these windows.
5. RRDP Repository
5.1. Unique Hostname
It is RECOMMENDED that the public RRDP Repository URIs use a hostname
different from both the [RFC8181] service_uri used by publishers, and
the hostname used in rsync URIs (sia_base).
Using a unique hostname will allow the operator to use dedicated
infrastructure and/or a Content Delivery Network for its RRDP content
without interfering with the other functions.
5.2. Bandwidth and Data Usage
The bandwidth needed for RRDP evolves and depends on many parameters.
These consist of three main groups:
1. RRDP-specific repository properties, such as the size of
notification-, delta-, and snapshot files.
2. Properties of the CAs publishing in a repository, such as the
number of updates, number of objects, and size of objects.
3. Relying party behaviour, e.g. using HTTP compression or not,
timeouts or minimum transfer speed for downloads, using
conditional HTTP requests for notification.xml.
When an RRDP repository server is overloaded, for example, if the
bandwidth demands exceed capacity, this causes a negative feedback
loop (i.e. the aggregate load increases), and the efficiency of RRDP
degrades. For example, when an RP attempts to download one or more
delta files, and one fails, it causes them to try to download the
snapshot (larger than the sum of the size of the deltas). If this
also fails, the RP falls back to rsync. Furthermore, when the RP
tries to use RRDP again on the next run, it typically starts by
downloading the snapshot.
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A Publication Server SHOULD attempt to prevent these issues by
closely monitoring performance (e.g. bandwidth, performance on an RP
outside their network, unexpected fallback to snapshot). Besides
increasing the capacity, we will discuss several other measures to
reduce bandwidth demands. Which measures are most effective is
situational.
5.2.1. Content Delivery Network
If possible, it is strongly RECOMMENDED that a Content Delivery
Network is used to serve the RRDP content. Care MUST BE taken to
ensure that the Notification File is not cached for longer than 1
minute unless the back-end RRDP Repository is unavailable, in which
case it is RECOMMENDED that stale files are served.
When using a CDN, it will likely cache 404s for files not found on
the back-end server. Because of this, the Publication Server SHOULD
use randomized, unpredictable paths for Snapshot and Delta Files to
avoid the CDN caching such 404s for future updates.
Alternatively, the Publication Server can delay writing the
notification file for this duration or clear the CDN cache for any
new files it publishes.
5.2.2. Limit Notification File Size
Nowadays, most RPs use conditional requests for notification files,
which reduces the traffic for repositories that do not often relative
to the update frequency of RPs. On the other hand, for repositories
that update frequently, the content uses the most traffic. For
example, for a large repository in January 2024, with a notification
file with 144 deltas covering 14 hours, the requests for the
notification file used 251GB out of 55.5TB/less than 0.5% of total
traffic during a period.
However, for some servers, this ratio may be different. [RFC8182]
stipulated that the sum of the size of deltas MUST not exceed the
snapshot size to avoid Relying Parties downloading more data than
necessary. However, this does not account for the size of the
notification file all RPs download. Keeping many deltas present may
allow RPs to recover more efficiently if they are significantly out
of sync. Still, including _all_ such deltas can also increase the
total data transfer because it increases the size of the notification
file.
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The Notification File size SHOULD be reduced by removing delta files
that have been available for a long time to prevent this situation.
Because some RPs will only update every 1-2 hours (in 2024), the
Publication Server SHOULD include deltas for at least 4 hours.
Furthermore, we RECOMMEND that Publication Servers do not produce
Delta Files more frequently than once per minute. A possible
approach for this is that the Publication Server SHOULD publish
changes at a regular (one-minute) interval. The Publication Server
then publishes the updates received from all Publishers in this
interval in a single RRDP Delta File.
While, the latter may not reduce the amount of data due to changed
objects, this will result in shorter notification files, and will
reduce the number of delta files that RPs need to fetch and process.
5.2.3. Manifest and CRL Update Times
The manifest and CRL next update time and expiry are determined by
the issuing CA rather than the Publication Server.
From the CA's point of view a longer period used between scheduled
Manifest and CRL re-issuance ensures that they will have more time to
resolve unforeseen operational issues. Their current RPKI objects
would still remain valid. On the other hand, CAs may wish to avoid
using excessive periods because it would make them vulnerable to RPKI
data replay attacks.
From the Publication Server's point of view shorter update times
result in more data churn due to manifest and CRL refreshes only. As
said, the choice is made by the CAs, but in certain setups -
particularly hosted RPKI services - it may be possible to tweak the
manifest and CRL re-signing timing. One large repository has found
that increasing the re-signing cycle from once every 24 hours, to
once every 48 hours (still deemed acceptable) reduced the data usage
with approximately 50% as most changes in the system are due to re-
signing rather than e.g. ROA changes.
5.3. Consistent load-balancing
5.3.1. Notification File Timing
Notification Files MUST NOT be available to RPs before the referenced
snapshot and delta files are available.
As a result, when using a load-balancing setup, care SHOULD be taken
to ensure that RPs that make multiple subsequent requests receive
content from the same node (e.g. consistent hashing). This way,
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clients view the timeline on one node where the referenced snapshot
and delta files are available. Alternatively, publication
infrastructure SHOULD ensure a particular ordering of the visibility
of the snapshot plus delta and notification file. All nodes should
receive the new snapshot and delta files before any node receives the
new notification file.
When using a load-balancing setup with multiple backends, each
backend MUST provide a consistent view and MUST update more
frequently than the typical refresh rate for rsync repositories used
by RPs. When these conditions hold, RPs observe the same RRDP
session with the serial monotonically increasing. Unfortunately,
[RFC8182] does not specify RP behavior if the serial regresses. A s
a result, some RPs download the snapshot to re-sync if they observe a
serial regression.
5.3.2. L4 load-balancing
If an RRDP repository uses L4 load-balancing, some load-balancer
implementations will keep connections to a node in the pool that is
no longer active (e.g. disabled because of maintenance). Due to HTTP
keepalive, requests from an RP (or CDN) may continue to use the
disabled node for an extended period. This issue is especially
prominent with CDNs that use HTTP proxies internally when connecting
to the origin while also load-balancing over multiple proxies. As a
result, some requests may use a connection to the disabled server and
retrieve stale content, while other connections load data from
another server. Depending on the exact configuration – (U+2013) for
example, nodes behind the LB may have different RRDP sessions –
(U+2013) this can lead to an inconsistent RRDP repository.
Because of this issue, we RECOMMEND to (1) limit HTTP keepalive to a
short period on the webservers in the pool and (2) limit the number
of HTTP requests per connection. When applying these
recommendations, this issue is limited (and effectively less
impactful when using a CDN due to caching) to a fail-over between
RRDP sessions, where clients also risk reading a notification file
for which some of the content is unavailable.
6. Rsync Repository
In this section, we will elaborate on the following recommendations:
* Use symlinks to provide consistent content
* Use deterministic timestamps for files
* Load balancing and testing
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6.1. Consistent Content
A naive implementation of the Rsync Repository might change the
repository content while RPs transfer files. Even when the
repository is consistent from the repository server's point of view,
clients may read an inconsistent set of files. Clients may get a
combination of newer and older files. This "phantom read" can lead
to unpredictable and unreliable results. While modern RPs will treat
such inconsistencies as a "Failed Fetch" ([RFC9286]), it is best to
avoid this situation since a failed fetch for one repository can
cause the rejection of the publication point for a sub-CA when
resources change.
One way to ensure that rsyncd serves connected clients (RPs) with a
consistent view of the repository is by configuring the rsyncd
'module' path to a path that contains a symlink that the repository-
writing process updates for every repository publication.
Following this process, when an update is published:
1. write the complete updated repository into a new directory
2. fix the timestamps of files (see next section)
3. change the symlink to point to the new directory
Multiple implementations implement this behavior ([krill-sync],
[rpki-core], [rsyncit], the rpki.apnic.net repositories, a supporting
shellscript [rsync-move]).
Because rsyncd resolves this symlink when it chdirs into the module
directory when a client connects, any connected RPs can read a
consistent state. To limit the amount of disk space a repository
uses, a Rsync Repository must clean up copies of the repository; this
is a trade-off between providing service to slow clients and disk
space.
A repository can safely remove old directories when no RP fetching at
a reasonable rate is reading that data. Since the last moment an RP
can start reading from a copy is when it last "current", the time a
client has to read a copy begins when it was last current (c.f. since
written).
Empirical data suggests that Rsync Repositories MAY assume it is safe
to do so after one hour. We recommend monitoring for "file has
vanished" lines in the rsync log file to detect how many clients are
affected by this cleanup process.
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6.2. Deterministic Timestamps
By default, rsync uses the modification time and file size to
determine if it should transfer a file. Therefore, throughout a
file's lifetime, the modification time SHOULD NOT change unless the
file's content changes.
We RECOMMEND the following deterministic heuristics for objects'
timestamps when written to disk. These heuristics assume that a CA
is compliant with [RFC9286] and uses "one-time-use" EE certificates:
* For CRLs, use the value of thisUpdate.
* For RPKI Signed Objects, use the CMS signing-time (see
([I-D.spaghetti-sidrops-cms-signing-time]))
* For CA and BGPSec Router Certificates, use the value of notBefore
* For directories, use any constant value.
6.3. Load Balancing and Testing
To increase availability, during both regular maintenance and
exceptional situations, a rsync repository that strives for high
availability should be deployed on multiple nodes load-balanced by an
L4 load-balancer. Because Rsync sessions use a single TCP connection
per session, there is no need for consistent load-balancing between
multiple rsyncd servers as long as they each provide a consistent
view. While it is RECOMMENDED that repositories are updated more
frequently than the typical refresh rate for rsync repositories used
by RPs to ensure that the repository continuously moves forward from
a client's point of view, breaking not holding this constraint does
not cause degraded behavior.
It is RECOMMENDED that the Rsync Repository is load tested to ensure
that it can handle the requests by all RPs in case they need to fall
back from using RRDP (as is currently preferred).
We RECOMMEND serving rsync repositories from local storage so the
host operating system can optimally use its I/O cache. Using network
storage is NOT RECOMMENDED because it may not benefit from this
cache. For example, when using NFS, the operating system cannot
cache the directory listing(s) of the repository.
We RECOMMENDED setting the "max connections" to a value that a single
node can handle with (1) the available memory and (2) the IO
performance available to be able to serve this number of connections
in the time RPs allow for rsync to fetch data. Load-testing results
show that machine memory is likely the limiting factor for large
repositories that are not IO limited.
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The number of rsyncd servers needed depends on the number of RPs,
their refresh rate, and the "max connections" used. These values are
subject to change over time, so we cannot give clear recommendations
here except to restate that we RECOMMEND load-testing rsync and re-
evaluating these parameters over time.
7. Single CA Repositories
Some delegated CAs in the RPKI use their own dedicated Repository.
Operating a small repository is much easier than operating a large
one. There may not be a need to use a CDN for RRDP because the
notification, snapshot and delta are relatively small. Also, the
performance issues of rscynd for recursive fetches are far less of a
problem for small and flat repositories.
Because RPs will use cached data, short outages don't need to cause
immediate issues if CAs fix their Repository before objects expire
and ensure that their Publication Server ([RFC8181]) is available
when there is a need to update RPKI objects such as ROAs.
However, availability issues with such repositories are frequent,
which can negatively impact Relying Party software. Therefore, it is
strongly RECOMMENDED that CAs use a publication service provided by
their RIR, NIR or other parent as much as possible. And it is
RECOMMENDED that CAs that act as a parent make a Publication Service
available to their children.
8. Acknowledgments
This document is the result of many informal discussions between
implementers.
The authors would like to thank Job Snijders for their helpful review
of this document.
9. Normative References
[I-D.spaghetti-sidrops-cms-signing-time]
Snijders, J. and T. Harrison, "On the use of the CMS
signing-time attribute in RPKI Signed Objects", Work in
Progress, Internet-Draft, draft-spaghetti-sidrops-cms-
signing-time-01, 7 June 2023,
<https://datatracker.ietf.org/doc/html/draft-spaghetti-
sidrops-cms-signing-time-01>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8181] Weiler, S., Sonalker, A., and R. Austein, "A Publication
Protocol for the Resource Public Key Infrastructure
(RPKI)", RFC 8181, DOI 10.17487/RFC8181, July 2017,
<https://www.rfc-editor.org/info/rfc8181>.
[RFC8182] Bruijnzeels, T., Muravskiy, O., Weber, B., and R. Austein,
"The RPKI Repository Delta Protocol (RRDP)", RFC 8182,
DOI 10.17487/RFC8182, July 2017,
<https://www.rfc-editor.org/info/rfc8182>.
[RFC9286] Austein, R., Huston, G., Kent, S., and M. Lepinski,
"Manifests for the Resource Public Key Infrastructure
(RPKI)", RFC 9286, DOI 10.17487/RFC9286, June 2022,
<https://www.rfc-editor.org/info/rfc9286>.
10. Informative References
[krill-sync]
Bruijnzeels, T., "krill-sync", 2023,
<https://github.com/NLnetLabs/krill-sync>.
[rpki-core]
Team, R., "rpki-core", 2023,
<https://github.com/RIPE-NCC/rpki-core>.
[rsync-move]
Snijders, J., "rpki-rsync-move.sh.txt", 2023,
<http://sobornost.net/~job/rpki-rsync-move.sh.txt>.
[rsyncit] Team, R., "rpki-core", 2023,
<https://github.com/RIPE-NCC/rsyncit>.
Authors' Addresses
Tim Bruijnzeels
RIPE NCC
Email: tim@ripe.net
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Ties de Kock
RIPE NCC
Email: tdekock@ripe.net
Frank Hill
ARIN
Email: frank@arin.net
Tom Harrison
APNIC
Email: tomh@apnic.net
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