slides: architecture, load balancing, redundancy
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figures/redundancy_ring.pdf
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id="tspan889-6">second redundancy level</tspan></text>
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After Width: | Height: | Size: 6.7 KiB |
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shell.nix
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shell.nix
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@ -29,6 +29,9 @@ mkShell {
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logreq
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koma-script
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xits
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stix
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stix2-otf
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stix2-type1
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opensans
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;
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@ -38,9 +41,9 @@ mkShell {
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};
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})
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biber
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opensans-ttf
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xits-math
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stix-otf
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#opensans-ttf
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#xits-math
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#stix-otf
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fontconfig
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# for instance DNS query script
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];
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# for font discovery
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FONTCONFIG_FILE = makeFontsConf { fontDirectories = [ lmodern opensans-ttf xits-math stix-otf ]; };
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FONTCONFIG_FILE = makeFontsConf { fontDirectories = [ lmodern texlive.opensans.pkgs texlive.stix.pkgs ]; };
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}
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talk-slides.tex
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talk-slides.tex
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\usepackage[backend=biber, sorting=none]{biblatex}
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\usepackage{ccicons}
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\usepackage{wrapfig}
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\usepackage{ifluatex}
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@ -298,14 +299,124 @@ Hashtags are used for marking posts about certain topics or events:
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\end{itemize}
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\end{frame}
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\begin{frame}{System Architecture}{adding a P2P backend to the fediverse}
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\begin{frame}{System Architecture}{adding a DHT backend to the fediverse}
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core idea: distributing responsibility for tags using a \textbf{D}istributed \textbf{H}ash \textbf{T}able \note{distribute responsibility for posts of a hashtag = relaying \& storage}
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core idea: distribute responsibility for tags among instances using a \textbf{D}istributed \textbf{H}ash \textbf{T}able, \note{distribute responsibility for posts of a hashtag = relaying \& storage}
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based on Chord
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\note[item]{DHT: structured P2P networks providing efficient (log N) key-value storage and lookup}
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\note[item]{self-organising, no central authority}
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\end{frame}
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\begin{frame}{System Architecture}{adding a DHT backend to the fediverse}
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\begin{columns}
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\begin{column}{0.4\textwidth}
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\begin{itemize}
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\item calculate hash value of keys and node IDs
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\item place these hashes onto the same circular name space
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\item each node keeps routing table of \(\log \#number\_nodes\) entries\note[item]{joining and leaving covered in paper}
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\end{itemize}
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\end{column}
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\begin{column}{0.6\textwidth}
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\includegraphics[height=0.62\paperheight]{figures/finger_table_routing_1.pdf}
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\end{column}
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\end{columns}
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\end{frame}
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\begin{frame}{System Architecture}{adding a DHT backend to the fediverse}
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\begin{columns}
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\begin{column}{0.55\textwidth}
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\begin{itemize}
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\item next nodeID \(\geq\) \texttt{hash(hashtag)} (mod keyspace size) is responsible for handling posts containing \texttt{hashtag}
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\item DHT used for iterative lookup of responsible relay/ storage node
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\end{itemize}
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\end{column}
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\begin{column}{0.45\textwidth}
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\includegraphics[height=0.62\paperheight]{figures/finger_table_routing_2.pdf}
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\end{column}
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\end{columns}
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\end{frame}
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\begin{frame}{Publishing, Relaying and Storage}{lifecycle of posts}
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\begin{enumerate}
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\item publishing instance looks up responsible relay instance on DHT for each included hashtag
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\item publishing instance sends post to responsible relay instance
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\item relay instance looks up responsible storage node on DHT
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\item relay instance verifies incoming post's signature, then relays post URI (ID) to all subscribers + storage node\note[item]{only post ID relayed, but not full post content. Reasons: LDSignatures not supported everywhere, deniability \& revocation}
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\item subscribing instances can now retrieve the full authenticated post from received post URI
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\end{enumerate}
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\end{frame}
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\begin{frame}{Publishing, Relaying and Storage}
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\begin{itemize}
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\item separate DHTs for relay and storage instances
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\item all actions after DHT lookup supposed to be done using ActivityPub via HTTPS
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\item subscription to hashtags/ querying posts is done at the responsible instance
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\end{itemize}
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\end{frame}
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\begin{frame}
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\note{so far so easy. But load distribution issues}
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\begin{itemize}
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\item node ID determines set of hashtags handled by instance
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\item problem: for security reasons, node \textbf{must not} choose their IDs freely
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\item Can instances be overloaded by their assigned hashtag posts?
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\end{itemize}
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\end{frame}
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\begin{frame}{Distribution of Posts per Tag}
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\includegraphics[width=0.49\textwidth]{statistics/twitter_hashtags_total.png}
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~
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\includegraphics[width=0.49\textwidth]{statistics/geraspora_hashtags_total.png}
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\note{analysis of a 1 month dump of Twitter, Geraspora (Diaspora) and Friendica posts\\
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Twitter: 70\% of posts used just once\\
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note the logarithmic axis!}
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distribution of posts per hashtag follows a steep power law
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\note{So what if a small node gets several large hashtags? => need for load balancing}
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\end{frame}
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\begin{frame}{Load Balancing}{of hashtags between nodes}
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\begin{itemize}
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\item \textit{k-choices} algorithm by Ledlie and Seltzer
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\item each node can choose from \(\kappa\) possible IDs
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\item nodes have a \textbf{capacity} and choose set of active IDs according to lowest mismatch of own and neighbour node capacity
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\item querying load of potential IDs before joining, periodic re-balancing
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\item independent load balancing of relay and storage nodes due to independent DHTs
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\end{itemize}
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% for Kolloquium, add simulation result
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\end{frame}
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\begin{frame}{Redundancy}
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\begin{columns}
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\begin{column}{0.55\textwidth}
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\begin{itemize}
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\item store redundant copies of hashtag data at equal distances on Chord ring\note{resilience against node failure, allows data validation through cross-checking}
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\item default redundancy: \(2^2 = 4\), scalable in powers of 2
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\item \textbf{relay nodes}: hot standby nodes take over in overload situations (load spikes)
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\item \textbf{storage nodes}: overloaded nodes can split stored posts by content hash and double redundancy set
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\end{itemize}
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\end{column}
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\begin{column}{0.45\textwidth}
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\includegraphics[width=\textwidth]{figures/redundancy_ring.pdf}
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\end{column}
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\end{columns}
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\end{frame}
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why even still use classic push federation?
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\section{Discussion}
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\begin{frame}{Discussion}{I need YOUR feedback}
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@ -322,6 +433,10 @@ CloudFlare
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load and capacity factor
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performance: batching, exponential back-off, no relayable sigs
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security: node ID derivation scheme
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\section{Summary}
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\begin{frame}{Summary}
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