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Every command in the shell is executed in a new AWS CLI instance - with parsers, command hierarchies, API specs and - more importantly _API clients_ - getting recreated for every command. 9 | 10 | == So what? 11 | 12 | It won't matter if you're running just one or two commands, but if you use `aws-cli` for automated batch processing, monitoring or periodic cleanup (like I do) you'll see major performance gains if you start reusing API clients (`boto` clients, in case of `aws-cli`). 13 | 14 | == How so? 15 | 16 | In the "regular" approach, each newly created API client has to establish a fresh network connection to the AWS API endpoint, which usually involves a DNS lookup and almost always a full https://security.stackexchange.com/questions/56623/avoiding-ssl-handshake-for-each-call[SSL handshake], wasting network bandwidth and adding a significant latency. 17 | 18 | Under the standard AWS CLI, this happens for every invocation (command); as each command spawns a new process, which does all this initialization and connectivity stuff, but then discards everything as the process dies at command completion. 19 | 20 | Additionally there's always the overhead of process spawning, loading of binaries, configs and https://github.com/boto/botocore/tree/master/botocore/data/[API definitions], dynamic https://github.com/boto/botocore/blob/master/botocore/client.py[generation] of `boto` client classes, initialization of parsers, command maps, https://github.com/boto/botocore/blob/master/botocore/hooks.py[event handlers], https://github.com/aws/aws-cli/blob/master/awscli/customizations/$$__init__.py$$[customizations] and god-knows-what-else stuff. While this overhead is quite acceptable for a few invocations, it can add up when you're batching hundreds of consecutive invocations. 21 | 22 | 23 | == So, what's the magic behind your `aws-cli-repl`? 24 | 25 | This REPL breaks the CLI into two components: a _client_ and a _daemon_ (just a background process, to be frank). 26 | 27 | === The client 28 | 29 | It simply: 30 | 31 | * accepts user commands (just like the user-facing portion of the CLI), 32 | * passes them to the daemon via a https://www.roman10.net/2011/04/21/named-pipe-in-linux-with-a-python-example/[named pipe], 33 | * reads the result from another named pipe and 34 | * shows it to the user. 35 | 36 | === The daemon 37 | 38 | This has the fun stuff. At launch, it: 39 | 40 | * initializes an https://github.com/aws/aws-cli/blob/master/awscli/clidriver.py[`awscli.CLIDriver`] instance 41 | * patches `$$__init__$$` and `invoke` on https://github.com/aws/aws-cli/blob/master/awscli/clidriver.py[`awscli.CLIOperationCaller`], to cache the `client` objects created during `invoke` 42 | 43 | Then it starts to loop: 44 | 45 | * point `sys.stdin` to the client's output pipe, and `sys.stdout` to its input pipe, 46 | * read user commands (piped by the client), 47 | * feed them to ``CLIDriver``'s `main` method, causing a CLI invocation, and 48 | * the CLI writes the output to `sys.stdout`, effectively piping it back to the client 49 | 50 | This way, the `CLIDriver` instance (and hence the clients cached by ``CLIOperationCaller``s) are kept alive throughout the life of the daemon, no matter how many times the client gets invoked; yielding all the benefits that we discussed before. 51 | 52 | === How does the daemon launch? 53 | 54 | During its first invocation, the REPL checks for the existence of the daemon in the system's https://stackoverflow.com/questions/46979567/find-processes-by-command-in-python[process list]. 55 | If it doesn't see one, it spawns a copy of itself, flagging it to run as the daemon - and continues its own journey as client, calling the new daemon via pipes as usual. 56 | 57 | So it effectively initializes itself during the first run, and remains alive as long as possible; consuming little resources (as it's only waiting to read from the named pipe). If it somehow gets killed, the next REPL invocation will spawn a new daemon. 58 | 59 | 60 | == Installation 61 | 62 | === Prerequisites 63 | 64 | * Python 2.7 or 3.x 65 | * https://github.com/aws/aws-cli[`awscli`] 66 | * https://github.com/giampaolo/psutil[`psutil`] (optional) 67 | 68 | === Installation 69 | 70 | Assuming the `awscli` module is resolvable by Python (e.g. via `PYTHONPATH`), simply 71 | 72 | * add `awsr` to the system `PATH`, and 73 | * make it executable. 74 | 75 | == Invocation 76 | 77 | `awsr` should work the same way as `aws` since it simply proxies everything to `aws`. 78 | 79 | ``` 80 | awsr ec2 describe-instances 81 | ``` 82 | 83 | Watch-mode commands that produce progressive output (like `ec2 wait instance-running`) may not work as expected (since the client does not receive output until the command execution completes). 84 | 85 | 86 | == What kind of improvement am I looking at? 87 | 88 | I don't have concrete figures (yet), but my first try with a batch deletion of https://docs.aws.amazon.com/AmazonCloudWatch/latest/logs/Working-with-log-groups-and-streams.html[CloudWatch log groups] was quite impressive. 89 | 90 | Deleting around 100 log groups via the standard `aws` command: 91 | 92 | * took around 4 minutes and 93 | * consumed around 1.6MB of data, 94 | * with DNS lookups and full SSL handshakes happening for every single request (verified via https://www.wireshark.org/[Wireshark]). 95 | 96 | Deleting around 150 log groups via `awsr`: 97 | 98 | * took around 2 minutes and 99 | * consumed less than 1MB of data, 100 | * with one initial DNS lookup, SSL handshakes limited to once per minute (could probably be further improved by tuning ``boto``'s connectivity options). 101 | 102 | Results may vary across AWS services and usage patterns, but I'm quite satisfied with what I've seen so far. 103 | 104 | 105 | == What's the catch? 106 | 107 | There's a lot: 108 | 109 | * As of now you cannot run multiple `awsr` commands in parallel, since the daemon doesn't distinguish between individual clients; it simply reads from and writes to the pipes. 110 | * Global parameters are not re-initialized for subsequent client calls. If you invoked it for `us-east-1` under profile `golum`, all subsequent commands executed by that daemon will run against the same region and profile. This can probably be avoided by invalidating or expanding the client cache; I'll need to look into that further. 111 | * `sys.stderr` is not redirected from daemon to client, so any errors (say, a S3 403 Forbidden) on the daemon will not be visible at the client - unless they're running in the same terminal window. 112 | * Some extensions like S3 don't seem to benefit from the caching - even when invoked against the same bucket. It needs further investigation. 113 | 114 | 115 | == Disclaimer 116 | 117 | No need to drag on with formalities; _you're on your own_. 118 | 119 | I will continue to experiment with `awsr` and attempt to fix issues as and when required (and possible), but it is still considered highly experimental and unstable :) 120 | 121 | 122 | == Contributing 123 | 124 | Feel free to report any issues that you encounter while using the tool; or, better still, submit a PR (after all, there's not even a hundred lines of code here so far :)) 125 | 126 | == License 127 | 128 | Copyright (C) 2018-2021 Janaka Bandara 129 | 130 | Licensed under the Apache License, Version 2.0 131 | -------------------------------------------------------------------------------- /awsr: -------------------------------------------------------------------------------- 1 | #!/usr/bin/python 2 | # Licensed under http://www.apache.org/licenses/LICENSE-2.0 3 | 4 | import os 5 | import sys 6 | import tempfile 7 | 8 | rd = tempfile.gettempdir() + "/awsr_rd" 9 | wr = tempfile.gettempdir() + "/awsr_wr" 10 | 11 | 12 | def run_client(): 13 | with open(rd, "w") as out: 14 | out.write(" ".join(sys.argv)) 15 | out.write("\n") 16 | if "-" in sys.argv: 17 | while True: 18 | data = sys.stdin.read(4096) 19 | if data == "": 20 | break 21 | out.write(data) 22 | 23 | last = None 24 | with open(wr, "r") as inp: 25 | while True: 26 | result = inp.read(4096) 27 | if len(result) == 0: 28 | break 29 | if last is not None: 30 | sys.stdout.write(last) 31 | sys.stdout.write(result[:-1]) 32 | last = result[-1:] 33 | return ord(last) 34 | 35 | 36 | def run_daemon(): 37 | from awscli.clidriver import CLIOperationCaller, LOG, create_clidriver, HISTORY_RECORDER 38 | 39 | def patchedInit(self, session): 40 | self._session = session 41 | self._client = None 42 | 43 | def patchedInvoke(self, service_name, operation_name, parameters, parsed_globals): 44 | if self._client is None: 45 | LOG.debug("Creating new %s client" % service_name) 46 | self._client = self._session.create_client( 47 | service_name, region_name=parsed_globals.region, 48 | endpoint_url=parsed_globals.endpoint_url, 49 | verify=parsed_globals.verify_ssl) 50 | client = self._client 51 | 52 | response = self._make_client_call( 53 | client, operation_name, parameters, parsed_globals) 54 | self._display_response(operation_name, response, parsed_globals) 55 | return 0 56 | 57 | CLIOperationCaller.__init__ = patchedInit 58 | CLIOperationCaller.invoke = patchedInvoke 59 | 60 | driver = create_clidriver() 61 | while True: 62 | with open(rd, "r") as inp: 63 | os.dup2(inp.fileno(), 0) 64 | args = bytes() 65 | while True: 66 | ch = os.read(inp.fileno(), 1) 67 | if ch == b"\n" or ch == b"": 68 | break 69 | args += ch 70 | args = args.decode("utf-8").split(" ")[1:] 71 | 72 | if len(args) > 0 and args[0] == "exit": 73 | sys.exit(0) 74 | 75 | sys.stdin = inp 76 | old_stdout = sys.stdout 77 | try: 78 | with open(wr, "w") as sys.stdout: 79 | try: 80 | rc = driver.main(args) 81 | except SystemExit as e: 82 | rc = 2 83 | # encode return code in the last byte of stdout 84 | sys.stdout.write(chr(rc)) 85 | 86 | HISTORY_RECORDER.record('CLI_RC', rc, 'CLI') 87 | except BrokenPipeError: 88 | pass 89 | sys.stdout = old_stdout 90 | 91 | 92 | def main(): 93 | if not os.access(rd, os.R_OK | os.W_OK): 94 | os.mkfifo(rd) 95 | if not os.access(wr, os.R_OK | os.W_OK): 96 | os.mkfifo(wr) 97 | 98 | if os.environ.get("AWSR_CLIENT") == "True": 99 | rc = run_client() 100 | sys.exit(rc) 101 | elif os.environ.get("AWSR_DAEMON") == "True": 102 | try: 103 | run_daemon() 104 | finally: 105 | os.remove(rd) 106 | os.remove(wr) 107 | return 108 | 109 | # fork if awsr daemon is not already running 110 | import psutil 111 | import subprocess 112 | ps = psutil.process_iter(attrs=["cmdline"]) 113 | procs = 0 114 | for p in ps: 115 | cmd = p.info["cmdline"] 116 | if cmd and len(cmd) > 1 and cmd[0].endswith("python") and cmd[1] == sys.argv[0]: 117 | procs += 1 118 | if procs < 2: 119 | sys.stderr.write("Forking new awsr background process\n") 120 | with open(os.devnull, 'r+b', 0) as DEVNULL: 121 | # new instance will see env var, and run itself as daemon 122 | p = subprocess.Popen(sys.argv, stdin=DEVNULL, stdout=DEVNULL, stderr=DEVNULL, close_fds=True, env={ 123 | "AWSR_DAEMON": "True", 124 | "AWS_PROFILE": os.environ.get("AWS_PROFILE", "default"), 125 | }) 126 | run_client() 127 | 128 | else: 129 | run_client() 130 | 131 | if __name__ == "__main__": 132 | main() 133 | --------------------------------------------------------------------------------