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\title{Garage}
\subtitle{a lightweight and robust geo-distributed data storage system}
\author{Alex Auvolat, Deuxfleurs}
\date{SEED webinar, 2024-01-12}
\begin{document}
% \begin{frame}
% \centering
% \includegraphics[width=.3\linewidth]{../../sticker/Garage.png}
% \vspace{1em}
%
% {\large\bf Alex Auvolat, Deuxfleurs Association}
% \vspace{1em}
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% \url{https://garagehq.deuxfleurs.fr/}
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% %Matrix channel: \texttt{\#garage:deuxfleurs.fr}
% \end{frame}
\begin{frame}
%\frametitle{Who I am}
\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}\\
Member of Deuxfleurs, lead developer of Garage
\end{column}
\begin{column}{.2\textwidth}
~
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\end{columns}
\vspace{.5em}
\begin{columns}[t]
\begin{column}{.2\textwidth}
\centering
\adjincludegraphics[width=.6\linewidth, valign=t]{../../logo/garage-notext.png}
\end{column}
\begin{column}{.6\textwidth}
\\\textbf{Garage}\\
A self-hosted alternative to S3 for object storage
\end{column}
\begin{column}{.2\textwidth}
~
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\end{columns}
\vspace{2em}
\begin{columns}[t]
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\centering
\adjincludegraphics[width=.5\linewidth, valign=t]{../assets/deuxfleurs.pdf}
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\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{Stable vs Resilient}
\hspace{1em}
\begin{minipage}{7cm}
\textbf{Building a "stable" system:}
\vspace{1em}
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}
$\to$ costly, only worth at DC scale\\
$\to$ still risk of DC-level incident...
\end{minipage}
\hfill
\begin{minipage}{7cm}
\textbf{Building a \underline{resilient} system:}
\vspace{1em}
An alternative, cheaper way:
\vspace{1em}
\begin{itemize}
\item Commodity hardware \\(e.g. old desktop PCs)
\vspace{.5em}
\item Commodity Internet \\(e.g. FTTB, FTTH) and power grid
\vspace{.5em}
\item \textbf{Geographical redundancy} \\(multi-site replication)
\end{itemize}
\vspace{1.5em}
\end{minipage}
\hspace{1em}
\end{frame}
\begin{frame}
\frametitle{Example: our infrastructure at Deuxfleurs}
\only<1>{
\begin{center}
\includegraphics[width=.8\linewidth]{../assets/neptune.jpg}
\end{center}
}
\only<2>{
\begin{center}
\includegraphics[width=.8\linewidth]{../assets/atuin.jpg}
\end{center}
}
\only<3>{
\begin{center}
\includegraphics[width=.8\linewidth]{../assets/inframap_jdll2023.pdf}
\end{center}
}
\end{frame}
\begin{frame}
\frametitle{Object storage: simpler than file systems}
\begin{minipage}{6cm}
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{minipage}
\hfill
\begin{minipage}{8cm}
\begin{center}
\vspace{2em}
\includegraphics[height=6em]{../2020-12-02_wide-team/img/Amazon-S3.jpg}
\hspace{2em}
\includegraphics[height=5em]{../assets/minio.png}
\vspace{2em}
\includegraphics[height=6em]{../../logo/garage_hires_crop.png}
\end{center}
\vspace{1em}
\end{minipage}
\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{Implementation: consensus vs weak consistency}
\hspace{1em}
\begin{minipage}{7cm}
\textbf{Consensus-based systems:}
\vspace{1em}
\begin{itemize}
\item \textbf{Leader-based:} a leader is elected to coordinate
all reads and writes
\vspace{1em}
\item Allows for \textbf{sequential reasoning}:
program as if running on a single machine
\vspace{1em}
\item Serializability is one of the \\
\textbf{strongest consistency guarantees}
\vspace{1em}
\item \textbf{Costly}, the leader is a bottleneck;
leader elections on failure take time
\end{itemize}
\end{minipage}
\hfill
\begin{minipage}{7cm} \visible<2->{
\textbf{Weakly consistent systems:}
\vspace{1em}
\begin{itemize}
\item \textbf{Nodes are equivalent}, any node
can originate a read or write operation
\vspace{1em}
\item \textbf{Operations must be independent},
conflicts are resolved after the fact
\vspace{1em}
\item Strongest achievable consistency:\\
\textbf{read-after-write consistency}\\(using quorums)
\vspace{1em}
\item \textbf{Fast}, no single bottleneck;\\
works transparently with offline nodes
\end{itemize}
} \end{minipage}
\hspace{1em}
\end{frame}
\begin{frame}
\frametitle{Why avoid consensus?}
Consensus can be implemented reasonably well in practice, so why avoid it?
\vspace{2em}
\begin{itemize}
\item \textbf{Software complexity:} RAFT and PAXOS are complex beasts;\\
harder to prove, harder to reason about
\vspace{1.5em}
\item \textbf{Performance issues:}
\vspace{1em}
\begin{itemize}
\item Taking a decision may take an \textbf{arbitrary number of steps} (in adverse scenarios)
\vspace{1em}
\item The leader is a \textbf{bottleneck} for all requests;\\
even in leaderless approaches, \textbf{all nodes must process all operations in order}
\vspace{1em}
\item Particularly \textbf{sensitive to higher latency} between nodes
\end{itemize}
\end{itemize}
\end{frame}
\begin{frame}
\frametitle{Objective: the right level of consistency for Garage}
\underline{Constraints:} slow network (geographical distance), node unavailability/crashes\\
\underline{Objective:} maximize availability, maintain an \emph{appropriate level of consistency}\\
\vspace{1em}
\begin{enumerate}
\item<2-> \textbf{Weak consistency for most things}\\
\vspace{1em}
\underline{Example:} \texttt{PutObject}\\
\vspace{.5em}
If two clients write the same
object at the same time, one of the two is implicitly overwritten.
No need to coordinate, use a \emph{last-writer-wins register}.
\vspace{1em}
\item<3-> \textbf{Stronger consistency only when necessary}\\
\vspace{1em}
\underline{Example:} \texttt{CreateBucket}\\
\vspace{.5em}
A bucket is a reserved name in a shared namespace,
two clients should be prevented from both creating the same bucket
(\emph{mutual exclusion}).
\end{enumerate}
\end{frame}
\begin{frame}
\frametitle{The possibility of \emph{leaderless consensus}}
Currently, Garage \emph{only has weak consistency}. Is fast, but \texttt{CreateBucket} is broken!
\visible<2->{
\vspace{1em}
Leaderless consensus (Antoniadis et al., 2023) alleviates issues with RAFT and PAXOS:
\vspace{1em}
\begin{itemize}
\item \textbf{No leader.} All nodes participate equally at each time step,
and different nodes can be unavailable at different times without issues.
\\ \vspace{.5em} $\to$ better tolerance to the high latency (remove bottleneck issue)
\\ $\to$ tolerates crash transparently
\vspace{1em}
\item \textbf{Simpler formalization.} The algorithm is very simple to express and to analyze in mathematical terms.
\end{itemize}
}
\visible<3->{
\vspace{1em}
One of the possible subjects for this PhD:
\\$\to$ \emph{integration of leaderless consensus in Garage} + testing + perf eval, etc.
}
\end{frame}
\begin{frame}
\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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