Running Chess Engines in the Cloud

On November 11th, Norway’s Magnus Carlsen will defend his chess world championship against Sergey Karjakin of Russia. The unified championship will return to New York and American soil for the first time since 1990, when two chess legends, Kasparov and Karpov, met for the last time in a world chess championship match. Since then, chess’ popularity in the United States has slowly increased, as has the strength of its players. Just two months ago, the United States men’s team won the 42nd Chess Olympiad for the first time in 40 years. They are now led by Top 10 players Caruana, So and Nakamura.

Nevertheless, World Champion Magnus Carlsen has dominated chess for the last 5 years and is rightfully in position to defend his world championship. In preparation for important tournaments like the world championship match, Grandmasters almost always hire a team of ‘seconds’ (other grandmasters) to assist them in preparation. Their main job is to analyze moves for the opening phase of the game to maximize the charted territory, if you will, of their player. One of the most important tools they use in this analysis is the computer engine. The computer engine is a piece of software which objectively evaluates any chess positions.

Top Chess Grandmasters have a bit of a love-hate relationship with computer chess engines. Although it has become an essential and invaluable tool for training and preparation, many lament the loss of creativity due to the extensive charting of opening sequences known as the opening book. Players take less risk in openings because a well-prepared opponent will easily expose creative but unsound ideas. The capacity for top Grandmasters to memorize the thousands of variation of an opening book then becomes a limiting factor. Some grandmasters, such as Carlsen, intentionally play moves early on which are less analyzed but also less optimal to be able to “just play chess” instead of challenging the opponent’s preparation and memorization skills.

Today, grandmasters and amateurs alike use chess engines for training and analysis. There are many different chess engines (some paid, some open source) which all essentially do the same thing which is to evaluate a chess position. When playing a game against a chess engine, for most beginners to intermediate players the “strength” of the engine is not important. An engine that runs on an iPhone can easily beat most amateur players. You’d have to artificially dial down the strength of the engine to get a competitive game. We have gotten to the point where chess engines can beat any human in a game with “classical time controls” (90 minutes for first 40 moves). The best chess engines have Elo scores of 3200+ while the highest achieved rating of any human player has been just shy of 2900. It is therefore no longer interesting for humans to compete against chess engines. Instead, there are now leagues which just feature chess engines, in which they compete against each other under fixed conditions.

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Jerauld, Brian. A Brief Postmortem. Digital image. ChessBase. Chessbase.com, 27 Apr. 2015. Web. 16 Nov. 2016.
2. f4 was a real cool move you played there, Garry. I think… Ok, let’s ask Stockfish

How it Works
Here is a very high level overview of how chess engines works.

There are three distinct stages within a chess game that can be handled differently by chess engines. The opening uses an opening book, a database of predefined lines of moves. Once the engine is “out of book” it will use its evaluation and tree search capabilities to find its best moves. Lastly in positions with few pieces on the board an engine can use an endgame tablebase which stores all winning moves for a given position on the board.

The most important part of a chess engine is its ability to evaluate a static position in the most efficient manner possible. It uses this evaluation in conjunction with a tree search to find the best move or moves possible in the current position. It can store evaluated positions in a hash table so it doesn’t have to recalculate a given position more than once. The deeper the engine can search the tree, theoretically, the more accurate its evaluation is of the current position and its ability to predict the best move.

What specific algorithms in engines makes a better chess engine is up for debate. In general, being able to search a tree faster is not useful if your static evaluation is inaccurate. For this reason you need to test engines against other engines or different versions of engines to make sure that incremental improvements have the desired effect. There are also competitions which pit engines against each other. TCEC is one of those competitions. These competitions accelerate the development of new evaluation techniques in chess engines.

In general, tree search is a fairly brute-force-ish way of evaluating a position even though there is a lot of complex theory behind optimizing this kind algorithm. Most chess engines today are therefore “dumb” tools. You give it a position and it evaluates it. When Grandmasters use it for preparation, there’s always a human in the loop to tell the engine what positions it needs to evaluate and to tell it when it should stop evaluating. A next step in development of chess engines is the inclusion of Artificial Intelligence (AI). As we saw in AlphaGo vs Lee Sedol, inclusion of AI in board game engines significantly increases its strength and utility. AI will allow players to use engines for a specific purposes. For example, we can study how a specific opponent reacts to certain positions, what their tendencies are and generate a strategy specifically for that opponent by feeding the engine all the games the opponent has ever played. At a high level we can learn from patterns in positions and correlate them to outcomes of games given the strength of each player. With the inclusion of these new technologies and increased strength of engines there is no doubt that the landscape of competitive chess will change.

Hardware Considerations
Today’s strongest engines do not parallelize well or not at all across multiple nodes because of the current state parallel tree search algorithms. Some attempts are been made to parallelize over multiple nodes using distributed process algorithms, but these versions are not being used extensively in the chess community. So, the approach today would be to analyze different positions on different instances of the chess engine using a human in the loop. The single-node limitation of many chess engines makes it such that large multi-core SMP machines can significantly outperform, say, a number of laptops networked together.

With the single node limitations of chess engines, clusters can still be used to do many evaluations in parallel for analyses. Clusters can also be used in developing chess engine software. Simulating many games or positions is one of the only ways to make sure that changes in engine code actually make it stronger.

How to Run a Chess Engine on Rescale
Rescale currently provides a framework for running UCI chess engines. It’s a bring-your-own engine setup. If you do not provide a chess engine, it will run Stockfish 7 by default.

Once you launch a job with the chess engine it will broadcast and listen on port 30000. You will need to set up an ssh tunnel to forward a local port to the analysis node port 30000. See the video below for a complete overview of how to run Stockfish on Rescale with the client Scid:

You can run any UCI engine. Make sure you name the engine executable “engine” and upload it as an input file. Rescale will automatically use the uploaded engine:

You can even run 2 engines against each other. If you wanted to run, say, Komodo against Stockfish. You would start two jobs on Rescale each running a different engine. Just make sure you forward a different local port to your second engine:

The key components of linking your UCI client to the engine running on Rescale are your ssh tunnel and your raw connection to the engine using either netcat (nc) on Linux/MacOS or plink.exe on Windows.

Armchair Chess QB
The transmission of live games with “live evaluation” on sites such as Chessbase or Chessbomb allows every chess enthusiast to be an armchair quarterback during tournaments such as the upcoming world championship. This year, take it a step further and do the analysis yourself using Chess Engines on Rescale.

This article was written by Mulyanto Poort.