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\title{Garage}
\subtitle{a lightweight and robust geo-distributed data storage system}
\author{Deuxfleurs Association}
\date{Inria, 2023-01-18}
\begin{document}
\begin{frame}
\centering
\includegraphics[width=.3\linewidth]{../../sticker/Garage.pdf}
\vspace{1em}
{\large\bf Deuxfleurs Association}
\vspace{1em}
\url{https://garagehq.deuxfleurs.fr/}
Matrix channel: \texttt{\#garage:deuxfleurs.fr}
\end{frame}
\begin{frame}
\frametitle{Who we are}
\begin{columns}[t]
\begin{column}{.2\textwidth}
\centering
\adjincludegraphics[width=.4\linewidth, valign=t]{assets/alex.jpg}
\end{column}
\begin{column}{.6\textwidth}
\textbf{Alex Auvolat}\\
PhD; co-founder of Deuxfleurs
\end{column}
\begin{column}{.2\textwidth}
~
\end{column}
\end{columns}
\vspace{1em}
\begin{columns}[t]
\begin{column}{.2\textwidth}
~
\end{column}
\begin{column}{.6\textwidth}
\textbf{Quentin Dufour}\\
PhD; co-founder of Deuxfleurs
\end{column}
\begin{column}{.2\textwidth}
\centering
\adjincludegraphics[width=.5\linewidth, valign=t]{assets/quentin.jpg}
\end{column}
\end{columns}
\vspace{2em}
\begin{columns}[t]
\begin{column}{.2\textwidth}
\centering
\adjincludegraphics[width=.5\linewidth, valign=t]{assets/deuxfleurs.pdf}
\end{column}
\begin{column}{.6\textwidth}
\textbf{Deuxfleurs}\\
A non-profit self-hosting collective,\\
member of the CHATONS network
\end{column}
\begin{column}{.2\textwidth}
\centering
\adjincludegraphics[width=.7\linewidth, valign=t]{assets/logo_chatons.png}
\end{column}
\end{columns}
\end{frame}
\begin{frame}
\frametitle{Our objective at Deuxfleurs}
\begin{center}
\textbf{Promote self-hosting and small-scale hosting\\
as an alternative to large cloud providers}
\end{center}
\vspace{2em}
\visible<2->{
Why is it hard?
}
\visible<3->{
\vspace{2em}
\begin{center}
\textbf{\underline{Resilience}}\\
{\footnotesize (we want good uptime/availability with low supervision)}
\end{center}
}
\end{frame}
\begin{frame}
\frametitle{How to make a \underline{stable} system}
Enterprise-grade systems typically employ:
\vspace{1em}
\begin{itemize}
\item RAID
\item Redundant power grid + UPS
\item Redundant Internet connections
\item Low-latency links
\item ...
\end{itemize}
\vspace{1em}
$\to$ it's costly and only worth it at DC scale
\end{frame}
\begin{frame}
\frametitle{How to make a \underline{resilient} system}
\only<1,4-5>{
Instead, we use:
\vspace{1em}
\begin{itemize}
\item \textcolor<2->{gray}{Commodity hardware (e.g. old desktop PCs)}
\vspace{.5em}
\item<4-> \textcolor<5->{gray}{Commodity Internet (e.g. FTTB, FTTH) and power grid}
\vspace{.5em}
\item<5-> \textcolor<6->{gray}{\textbf{Geographical redundancy} (multi-site replication)}
\end{itemize}
}
\only<2>{
\begin{center}
\includegraphics[width=.8\linewidth]{assets/atuin.jpg}
\end{center}
}
\only<3>{
\begin{center}
\includegraphics[width=.8\linewidth]{assets/neptune.jpg}
\end{center}
}
\only<6>{
\begin{center}
\includegraphics[width=.5\linewidth]{assets/inframap.jpg}
\end{center}
}
\end{frame}
\begin{frame}
\frametitle{How to make this happen}
\begin{center}
\only<1>{\includegraphics[width=.8\linewidth]{assets/slide1.png}}%
\only<2>{\includegraphics[width=.8\linewidth]{assets/slide2.png}}%
\only<3>{\includegraphics[width=.8\linewidth]{assets/slide3.png}}%
\end{center}
\end{frame}
\begin{frame}
\frametitle{Distributed file systems are slow}
File systems are complex, for example:
\vspace{1em}
\begin{itemize}
\item Concurrent modification by several processes
\vspace{1em}
\item Folder hierarchies
\vspace{1em}
\item Other requirements of the POSIX spec
\end{itemize}
\vspace{1em}
Coordination in a distributed system is costly
\vspace{1em}
Costs explode with commodity hardware / Internet connections\\
{\small (we experienced this!)}
\end{frame}
\begin{frame}
\frametitle{A simpler solution: object storage}
Only two operations:
\vspace{1em}
\begin{itemize}
\item Put an object at a key
\vspace{1em}
\item Retrieve an object from its key
\end{itemize}
\vspace{1em}
{\footnotesize (and a few others)}
\vspace{1em}
Sufficient for many applications!
\end{frame}
\begin{frame}
\frametitle{A simpler solution: object storage}
\begin{center}
\includegraphics[height=6em]{../2020-12-02_wide-team/img/Amazon-S3.jpg}
\hspace{3em}
\includegraphics[height=5em]{assets/minio.png}
\hspace{3em}
\includegraphics[height=6em]{../../logo/garage_hires_crop.png}
\end{center}
\vspace{1em}
S3: a de-facto standard, many compatible applications
\vspace{1em}
MinIO is self-hostable but not suited for geo-distributed deployments
\vspace{1em}
\textbf{Garage is a self-hosted drop-in replacement for the Amazon S3 object store}
\end{frame}
\begin{frame}
\frametitle{The data model of object storage}
Object storage is basically a key-value store:
\vspace{1em}
\begin{center}
\begin{tabular}{|l|p{8cm}|}
\hline
\textbf{Key: file path + name} & \textbf{Value: file data + metadata} \\
\hline
\hline
\texttt{index.html} &
\texttt{Content-Type: text/html; charset=utf-8} \newline
\texttt{Content-Length: 24929} \newline
\texttt{<binary blob>} \\
\hline
\texttt{img/logo.svg} &
\texttt{Content-Type: text/svg+xml} \newline
\texttt{Content-Length: 13429} \newline
\texttt{<binary blob>} \\
\hline
\texttt{download/index.html} &
\texttt{Content-Type: text/html; charset=utf-8} \newline
\texttt{Content-Length: 26563} \newline
\texttt{<binary blob>} \\
\hline
\end{tabular}
\end{center}
\end{frame}
\begin{frame}
\frametitle{Two big problems}
\begin{enumerate}
\item \textbf{How to place data on different nodes?}\\
\vspace{1em}
\underline{Constraints:} heterogeneous hardware\\
\underline{Objective:} $n$ copies of everything, maximize usable capacity, maximize resilience\\
\vspace{1em}
$\to$ the Dynamo model + optimization algorithms
\vspace{2em}
\item<2-> \textbf{How to guarantee consistency?}\\
\vspace{1em}
\underline{Constraints:} slow network (geographical distance), node unavailability/crashes\\
\underline{Objective:} maximize availability, read-after-write guarantee\\
\vspace{1em}
$\to$ CRDTs, monotonicity, read and write quorums
\end{enumerate}
\end{frame}
\section{Problem 1: placing data}
\begin{frame}
\frametitle{Key-value stores, upgraded: the Dynamo model}
\textbf{Two keys:}
\begin{itemize}
\item Partition key: used to divide data into partitions (shards)
\item Sort key: used to identify items inside a partition
\end{itemize}
\vspace{1em}
\begin{center}
\begin{tabular}{|l|l|p{3cm}|}
\hline
\textbf{Partition key: bucket} & \textbf{Sort key: filename} & \textbf{Value} \\
\hline
\hline
\texttt{website} & \texttt{index.html} & (file data) \\
\hline
\texttt{website} & \texttt{img/logo.svg} & (file data) \\
\hline
\texttt{website} & \texttt{download/index.html} & (file data) \\
\hline
\hline
\texttt{backup} & \texttt{borg/index.2822} & (file data) \\
\hline
\texttt{backup} & \texttt{borg/data/2/2329} & (file data) \\
\hline
\texttt{backup} & \texttt{borg/data/2/2680} & (file data) \\
\hline
\hline
\texttt{private} & \texttt{qq3a2nbe1qjq0ebbvo6ocsp6co} & (file data) \\
\hline
\end{tabular}
\end{center}
\end{frame}
\begin{frame}
\frametitle{Key-value stores, upgraded: the Dynamo model}
\begin{itemize}
\item Data with different partition keys is stored independantly,\\
on a different set of nodes\\
\vspace{.5em}
$\to$ no easy way to list all partition keys\\
$\to$ no cross-shard transactions\\
\vspace{2em}
\item Placing data: hash the partition key, select nodes accordingly\\
\vspace{.5em}
$\to$ distributed hash table (DHT)
\vspace{2em}
\item For a given value of the partition key, items can be listed using their sort keys
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{How to spread files over different cluster nodes?}
\textbf{Consistent hashing (Dynamo):}
\vspace{1em}
\begin{center}
\only<1>{\includegraphics[width=.40\columnwidth]{assets/consistent_hashing_1.pdf}}%
\only<2>{\includegraphics[width=.40\columnwidth]{assets/consistent_hashing_2.pdf}}%
\only<3>{\includegraphics[width=.40\columnwidth]{assets/consistent_hashing_3.pdf}}%
\only<4>{\includegraphics[width=.40\columnwidth]{assets/consistent_hashing_4.pdf}}%
\end{center}
\end{frame}
\begin{frame}
\frametitle{Constraint: location-awareness}
\begin{center}
\includegraphics[width=\linewidth]{assets/location-aware.png}
\end{center}
\vspace{2em}
Garage replicates data on different zones when possible
\end{frame}
\begin{frame}
\frametitle{Constraint: location-awareness}
\begin{center}
\includegraphics[width=.8\linewidth]{assets/map.png}
\end{center}
\end{frame}
\begin{frame}
\frametitle{Issues with consistent hashing}
\begin{itemize}
\item Consistent hashing doesn't dispatch data based on geographical location of nodes
\vspace{1em}
\item<2-> Geographically aware adaptation, try 1:\\
data quantities not well balanced between nodes
\vspace{1em}
\item<3-> Geographically aware adaptation, try 2:\\
too many reshuffles when adding/removing nodes
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{How to spread files over different cluster nodes?}
\textbf{Garage's method: build an index table}
\vspace{1em}
Realization: we can actually precompute an optimal solution
\vspace{1em}
\visible<2->{
\begin{center}
\begin{tabular}{|l|l|l|l|}
\hline
\textbf{Partition} & \textbf{Node 1} & \textbf{Node 2} & \textbf{Node 3} \\
\hline
\hline
Partition 0 & Io (jupiter) & Drosera (atuin) & Courgette (neptune) \\
\hline
Partition 1 & Datura (atuin) & Courgette (neptune) & Io (jupiter) \\
\hline
Partition 2 & Io(jupiter) & Celeri (neptune) & Drosera (atuin) \\
\hline
\hspace{1em}$\vdots$ & \hspace{1em}$\vdots$ & \hspace{1em}$\vdots$ & \hspace{1em}$\vdots$ \\
\hline
Partition 255 & Concombre (neptune) & Io (jupiter) & Drosera (atuin) \\
\hline
\end{tabular}
\end{center}
}
\vspace{1em}
\visible<3->{
The index table is built centrally using an optimal algorithm,\\
then propagated to all nodes
}
\end{frame}
\begin{frame}
\frametitle{The relationship between \emph{partition} and \emph{partition key}}
\begin{center}
\begin{tabular}{|l|l|l|l|}
\hline
\textbf{Partition key} & \textbf{Partition} & \textbf{Sort key} & \textbf{Value} \\
\hline
\hline
\texttt{website} & Partition 12 & \texttt{index.html} & (file data) \\
\hline
\texttt{website} & Partition 12 & \texttt{img/logo.svg} & (file data) \\
\hline
\texttt{website} & Partition 12 &\texttt{download/index.html} & (file data) \\
\hline
\hline
\texttt{backup} & Partition 42 & \texttt{borg/index.2822} & (file data) \\
\hline
\texttt{backup} & Partition 42 & \texttt{borg/data/2/2329} & (file data) \\
\hline
\texttt{backup} & Partition 42 & \texttt{borg/data/2/2680} & (file data) \\
\hline
\hline
\texttt{private} & Partition 42 & \texttt{qq3a2nbe1qjq0ebbvo6ocsp6co} & (file data) \\
\hline
\end{tabular}
\end{center}
\vspace{1em}
\textbf{To read or write an item:} hash partition key
\\ \hspace{5cm} $\to$ determine partition number (first 8 bits)
\\ \hspace{5cm} $\to$ find associated nodes
\end{frame}
\begin{frame}
\frametitle{Garage's internal data structures}
\centering
\includegraphics[width=.75\columnwidth]{assets/garage_tables.pdf}
\end{frame}
\begin{frame}
\frametitle{Storing and retrieving files}
\begin{center}
\only<1>{\includegraphics[width=.45\linewidth]{assets/garage2a.drawio.pdf}}%
\only<2>{\includegraphics[width=.45\linewidth]{assets/garage2b.drawio.pdf}}%
\end{center}
\end{frame}
\section{Problem 2: ensuring consistency}
%\begin{frame}
% \frametitle{Garage's architecture}
% \begin{center}
% \includegraphics[width=.35\linewidth]{assets/garage.drawio.pdf}
% \end{center}
%\end{frame}
\begin{frame}
\frametitle{Garage is \emph{coordination-free}:}
\begin{itemize}
\item No Raft or Paxos
\vspace{1em}
\item Internal data types are CRDTs
\vspace{1em}
\item All nodes are equivalent (no master/leader/index node)
\end{itemize}
\vspace{2em}
$\to$ less sensitive to higher latencies between nodes
\end{frame}
\begin{frame}
\frametitle{Consistency model}
\begin{itemize}
\item Not ACID (not required by S3 spec) / not linearizable
\vspace{1em}
\item \textbf{Read-after-write consistency}\\
{\footnotesize (stronger than eventual consistency)}
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Impact on performances}
\begin{center}
\includegraphics[width=.8\linewidth]{assets/endpoint-latency-dc.png}
\end{center}
\end{frame}
\begin{frame}
\frametitle{An ever-increasing compatibility list}
\begin{center}
\includegraphics[width=.7\linewidth]{assets/compatibility.png}
\end{center}
\end{frame}
\begin{frame}
\frametitle{Further plans for Garage}
\begin{center}
\only<1>{\includegraphics[width=.8\linewidth]{assets/slideB1.png}}%
\only<2>{\includegraphics[width=.8\linewidth]{assets/slideB2.png}}%
\only<3>{\includegraphics[width=.8\linewidth]{assets/slideB3.png}}%
\end{center}
\end{frame}
\begin{frame}
\frametitle{K2V Design}
\begin{itemize}
\item A new, custom, minimal API
\vspace{1em}
\item<2-> Exposes the partitoning mechanism of Garage\\
K2V = partition key / sort key / value (like Dynamo)
\vspace{1em}
\item<3-> Coordination-free, CRDT-friendly (inspired by Riak)\\
\vspace{1em}
\item<4-> Cryptography-friendly: values are binary blobs
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Application: an e-mail storage server}
\begin{center}
\only<1>{\includegraphics[width=.9\linewidth]{assets/aerogramme.png}}%
\end{center}
\end{frame}
\begin{frame}
\frametitle{Aerogramme data model}
\begin{center}
\only<1>{\includegraphics[width=.4\linewidth]{assets/aerogramme_datatype.drawio.pdf}}%
\only<2->{\includegraphics[width=.9\linewidth]{assets/aerogramme_keys.drawio.pdf}\vspace{1em}}%
\end{center}
\visible<3->{Aerogramme encrypts all stored values for privacy\\
(Garage server administrators can't read your mail)}
\end{frame}
\begin{frame}
\frametitle{Different deployment scenarios}
\begin{center}
\only<1>{\includegraphics[width=.9\linewidth]{assets/aerogramme_components1.drawio.pdf}}%
\only<2>{\includegraphics[width=.9\linewidth]{assets/aerogramme_components2.drawio.pdf}}%
\end{center}
\end{frame}
\begin{frame}
\frametitle{A new model for building resilient software}
\begin{itemize}
\item Design a data model suited to K2V\\
{\footnotesize (see Cassandra docs on porting SQL data models to Cassandra)}
\vspace{1em}
\begin{itemize}
\item Use CRDTs or other eventually consistent data types (see e.g. Bayou)
\vspace{1em}
\item Store opaque binary blobs to provide End-to-End Encryption\\
\end{itemize}
\vspace{1em}
\item Store big blobs (files) in S3
\vspace{1em}
\item Let Garage manage sharding, replication, failover, etc.
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Research perspectives}
\begin{itemize}
\item Write about Garage's global architecture \emph{(paper in progress)}
\vspace{1em}
\item Measure and improve Garage's performances
\vspace{1em}
\item Discuss the optimal layout algorithm, provide proofs
\vspace{1em}
\item Write about our proposed architecture for (E2EE) apps over K2V+S3
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Where to find us}
\begin{center}
\includegraphics[width=.25\linewidth]{../../logo/garage_hires.png}\\
\vspace{-1em}
\url{https://garagehq.deuxfleurs.fr/}\\
\url{mailto:garagehq@deuxfleurs.fr}\\
\texttt{\#garage:deuxfleurs.fr} on Matrix
\vspace{1.5em}
\includegraphics[width=.06\linewidth]{assets/rust_logo.png}
\includegraphics[width=.13\linewidth]{assets/AGPLv3_Logo.png}
\end{center}
\end{frame}
\end{document}
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