Proxy server¶

This page describes the proxy server, a readonly frontend to mavkit-node which is designed to lower the load of full nodes. It can be run separately from a node and will handle some RPC requests by itself. It is named after two things:

The proxy mode of the client on which it builds upon.
Regular HTTP proxies, as proxy servers are meant to be deployed in front of a node, to lower the node’s load.

Even though the proxy server only serves a subset of the RPCs a full node can serve (detailed below), it can transparently act as a replacement for a full node, by redirecting to the node the HTTP requests that it cannot handle itself, as described below.

Launching a proxy server¶

The proxy server is implemented by the mavkit-proxy-server executable. The minimal arguments to the proxy server are --endpoint and --rpc-addr:

--endpoint specifies the URL of the RPC server of the underlying node, that is uses for obtaining data (via RPCs of the form /chains/<chain_id>/blocks/<block_id>/context/raw/bytes), and for redirecting the requests it cannot handle.
--rpc-addr specifies the URL that the proxy server should serve.

An important option is --data-dir:

--data-dir specifies the directory of the node from which to obtain data directly (without RPCs). Of course, this option can only be used when the proxy server has access to the node’s data directory. In this case, the proxy server will reduce the number of RPC calls to the node, thereby reducing its I/O consumption.

The full command-line API is detailed below.

Examples with the sandbox¶

In this section, we show examples of using a proxy server in the sandboxed node. For convenience, we repeat instructions for the sandboxed mode here, but refer the reader to the sandboxed mode page for further details.

In a first terminal, start a sandboxed node:

$ ./src/bin_node/mavkit-sandboxed-node.sh 1 --connections 1
  April 21 11:05:32.789 - node.config.validation: the node configuration has been successfully validated.
  Created /tmp/mavkit-node.Uzq5aGAN/config.json for network: sandbox.
  ...

Note in the trace above that the sandbox node wrote some configuration file in a working directory, that you may need to know later on.

Leave this first terminal running. In a second terminal, prepare the appropriate environment for running a proxy server:

$ eval `./src/bin_client/mavkit-init-sandboxed-client.sh 1`
$ mavkit-activate-alpha
$ mavkit-client bake for bootstrap1

To avoid warnings being printed in upcoming commands (optional):

$ export MAVRYK_CLIENT_UNSAFE_DISABLE_DISCLAIMER=y

You’re now ready to run a proxy server, as shown below. We specify debug variables in MAVRYK_LOG to see what the proxy server is doing (see the proxy mode page for more details).

$ export MAVRYK_LOG="proxy_rpc_ctxt->debug; proxy_rpc->debug; proxy_server_run->debug; proxy_getter->debug; proxy_services->debug"
$ ./mavkit-proxy-server --endpoint http://127.0.0.1:18731 --rpc-addr http://127.0.0.1:18732
  Apr 21 11:09:22.092 - proxy_server_run: starting proxy RPC server on 127.0.0.1:18732

Now, start a third terminal, and ask the client to request data from the proxy server:

$ export MAVRYK_CLIENT_UNSAFE_DISABLE_DISCLAIMER=y
$ ./mavkit-client --endpoint http://127.0.0.1:18732 rpc get /chains/main/blocks/head/context/contracts
  [ "mv1V73YiKvinVumxwvYWjCZBoT44wqBNhta7",
    "mv1S14SxfuavHMGDXxZJoBERZafLTyX3Z6Dx",
    "mv1TxMEnmav51G1Hwcib1rBnBeniDMgG8nkJ",
    "mv18Cw7psUrAAPBpXYd9CtCpHg9EgjHP9KTe",
    "mv1PVMnW8iyYxCoqLfPAha8EAPRxjTx7wqbn" ]

In the proxy server’s terminal, you should see this output (tree sizes may vary):

Apr 21 11:10:07.474 - proxy_rpc: chains/<main>/blocks/<head>/header
Apr 21 11:10:07.474 - proxy_rpc: proxy cache created for chain main and block head
Apr 21 11:10:07.476 - proxy_getter: Cache miss: (v1/constants)
Apr 21 11:10:07.476 - proxy_getter: split_key heuristic triggers, getting v1 instead of v1/constants
Apr 21 11:10:07.476 - proxy_rpc: /chains/<main>/blocks/<head>/context/raw/bytes/v1
Apr 21 11:10:07.477 - proxy_rpc: received tree of size 2
Apr 21 11:10:07.477 - proxy_getter: Cache hit: (v1/cycle_eras)
Apr 21 11:10:07.477 - proxy_getter: Cache miss: (pending_migration_balance_updates)
Apr 21 11:10:07.477 - proxy_rpc: /chains/<main>/blocks/<head>/context/raw/bytes/pending_migration_balance_updates
Apr 21 11:10:07.477 - proxy_getter: Cache miss: (pending_migration_operation_results)
Apr 21 11:10:07.477 - proxy_rpc: /chains/<main>/blocks/<head>/context/raw/bytes/pending_migration_operation_results
Apr 21 11:10:07.478 - proxy_getter: Cache miss: (contracts/index)
Apr 21 11:10:07.478 - proxy_rpc: /chains/<main>/blocks/<head>/context/raw/bytes/contracts/index
Apr 21 11:10:07.479 - proxy_rpc: received tree of size 115

Lines of the form proxy_rpc: /chains/<main>/blocks/<head>/context/raw/bytes/... show requests that the proxy server sends to the node to obtain data.

Now, in the third terminal, retrieve the contracts again:

$ ./mavkit-client --endpoint http://127.0.0.1:18732 rpc get /chains/main/blocks/head/context/contracts
  [ "mv1V73YiKvinVumxwvYWjCZBoT44wqBNhta7",
    "mv1S14SxfuavHMGDXxZJoBERZafLTyX3Z6Dx",
    "mv1TxMEnmav51G1Hwcib1rBnBeniDMgG8nkJ",
    "mv18Cw7psUrAAPBpXYd9CtCpHg9EgjHP9KTe",
    "mv1PVMnW8iyYxCoqLfPAha8EAPRxjTx7wqbn" ]
$ ./mavkit-client --endpoint http://127.0.0.1:18732 rpc get /chains/main/blocks/head/context/contracts
  # ... same output ...

In the meantime, in the proxy server’s terminal, you should see:

Apr 21 11:14:06.511 - proxy_getter: Cache hit: (v1/constants)
Apr 21 11:14:06.512 - proxy_getter: Cache hit: (v1/cycle_eras)
Apr 21 11:14:06.512 - proxy_getter: Cache hit: (pending_migration_balance_updates)
Apr 21 11:14:06.512 - proxy_getter: Cache hit: (pending_migration_operation_results)
Apr 21 11:14:06.512 - proxy_getter: Cache hit: (contracts/index)

This show that the proxy server is answering the request without delegating anything to the node: there is no proxy_rpc line. The proxy server is reusing the data it obtained for <head> from the first request.

Reducing RPC calls: `--data-dir`¶

To make the proxy server read the node’s data-dir instead of doing /chains/<main>/blocks/<head>/context/raw/bytes RPC calls, kill the proxy server you have launched above), and restart it as follows:

$ ./mavkit-proxy-server --endpoint http://127.0.0.1:18731 --rpc-addr http://127.0.0.1:18732 --data-dir <node_data_dir>
  protocol of proxy unspecified, using the node's protocol: ProtoALphaALphaALphaALphaALphaALphaALphaALphaDdp3zK
  Apr 21 11:09:22.092 - proxy_server_run: starting proxy RPC server on 127.0.0.1:18732

You can obtain the value for the --data-dir argument by looking at the output of the terminal where mavkit-node was launched (see above).

Now, in the third terminal (the client’s terminal), redo the request to retrieve contracts:

$ ./mavkit-client --endpoint http://127.0.0.1:18732 rpc get /chains/main/blocks/head/context/contracts
  # ... same output as above ...

Now the output in the proxy server terminal should be:

Apr 21 11:22:44.359 - proxy_rpc: chains/<main>/blocks/<head>/header
Apr 21 11:22:44.360 - proxy_rpc: proxy cache created for chain main and block head

There are far fewer proxy_rpc lines! That is because the proxy server obtained its data by reading the node’s data-dir, instead of performing RPC calls.

Additional arguments¶

We describe the entire list of options and arguments of the proxy server, also available in more concise form in the Proxy server manual:

-c and --config specify the JSON file to use an input for the configuration. This JSON file is an object like this: {"endpoint": "http://127.0.0.1:18731", "rpc_addr": "http://127.0.0.1:18732", "sym_block_caching_time": 60}. This file can specify all command line arguments except -l/--log-requests. If an argument if specified both in the configuration file and on the command line, the command line takes precedence.
-d and --data-dir specify the path of the data directory of the node. If specified, the proxy server obtains data by reading the disk instead of performing the /chains/<chain_id>/blocks/<block_id>/context/raw/bytes RPC. If possible (i.e. if the proxy server can access the node’s disk), this option should be used, because it reduces IO consumption of the node.

Note that this argument doesn’t make --endpoint optional, because the proxy server still needs to do RPC calls to obtain block headers. Further work removing all RPC calls is described in issue 2502.
-E and --endpoint specify the URL of the RPC server of the node to do requests to obtain data (RPCs of the form /chains/<chain_id>/blocks/<block_id>/context/raw/bytes).
-l and --log-requests specify to print the requests that are delegated to the node, in a verbose manner.
--rpc-addr specifies the URL that the proxy server should serve.
--rpc-tls specifies that the proxy server must use TLS. It should be a string of the form crt_file,key_file where crt_file is the path to the TLS certificate to use and key_file is the path to the key to use.
--sym-block-caching-time specifies the duration during which data for a symbolic block identifier (like head, head~1) is kept. Smaller values increase the endpoint’s load but yield more up-to-date to clients. Higher values decrease the endpoint’s load but make clients observe slightly deprecated values. If omitted, the value is defaulted to time_between_blocks. As time_between_blocks is hence regularly requested from the node, this incurs a higher load of the node.

All these options can either be specified in the configuration file or on the command line. However, the union of the configuration file and the command line should specify the endpoint to use and the RPC address to serve.

Supported RPCs¶

The proxy server itself only serves protocol-specific RPCs (listed here for protocol Alpha), but not all of them: since the proxy server is a readonly frontend for the underlying node, it only serves the readonly requests (GET requests, as well as a subset of the POST requests).

Because computations done by the proxy server are protocol-dependent, the proxy mode must choose a specific protocol: the same as the underlying node. However, the proxy mode does not support all protocols. Execute mavkit-client list proxy protocols to see the supported protocols. It is expected that, at any given time, the proxy server supports Alpha, the current protocol of Mainnet and the current protocol proposal on Mainnet at the time of release.

Unsupported RPCs¶

Requests that are not readonly can only be handled by a full node. However, the proxy server accepts any RPC: if the RPC is not supported by the proxy server, it will redirect clients to the appropriate endpoint on the underlying node using an HTTP redirect (301 Moved Permanently), and the node will then handle the request.

This can be easily demonstrated with a simple test: start a proxy server, and make a request to it with curl -vL <proxy server endpoint>/<any node-only RPC>. For example:

curl -vL http://127.0.0.1:18732/chains/main/blocks/head/header

The output from curl will show that the proxy server asks curl to follow a redirect to the node’s endpoint, which it will do because of the -L flag, and then it is finally responded to by the node. Any RPC that can be handled by the proxy server itself will of course not show this behaviour.

Clearly, making such requests to the proxy server does not decrease the load of the node. However, it does allow the use of a single endpoint for all RPC requests, which may be convenient for some use cases. In turn, it adds a slight delay to the HTTP request, unless the redirect is cached by the client.

Deployment¶

As a proxy server is a readonly frontend to a node, you can spawn multiple proxy servers in front of a single node.

As described above, the proxy server configures himself to the same protocol as the underlying node. As a consequence, when the underlying node changes protocol, the proxy server will also switch to the new protocol, unless the proxy server executable does not contain the new protocol. This may happen, for instance, if the executable was compiled before this protocol was even injected. As there is no dynamic linking of new protocols in the proxy server, it will start failing for RPCs concerning blocks of the new protocol. The solution in this case is to restart the proxy server using a more recent executable.

More generally, we recommend to automatically restart proxy servers that have a high ratio of failures. Restarting a proxy server is always fine; they can be thrown away at any moment.

Heuristics¶

The proxy server uses several heuristics to optimize its own work and/or decrease the node’s load. For example, there is a heuristic to make big map queries faster, which is useful when many queries to siblings keys of a given big map are done in burst.

The heuristics for protocol Alpha are implemented in file proxy.ml , in function split_key and associates. For example, any request of the form big_maps/index/i/contents/tail is transformed into a request of the form big_maps/index/i/contents to obtain data for all possible values of tail at once. For the moment, the heuristics cannot be specified on the command line, but this can be implemented in the future.