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Yutaro Mori
Yutaro Mori

Posted on • Edited on • Originally published at dev.to

I use cw, which is OSS to tail AWS CloudWatch Logs

#aws #cloudwatch #opensource #tutorial

Introduction

I will share cw, OSS to help to tail CloudWatch Logs.

Prerequisite knowledge

AWS CLI has a command which tails the logs collected CloudWatch Logs.

$ aws logs tail access_log
2021-07-22T07:45:55.422000+00:00 wordpress1 18.207.253.146 - - [22/Jul/2021:07:45:54 +0000] "GET /.env HTTP/1.1" 404 196 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36"
2021-07-22T07:45:59.986000+00:00 wordpress1 18.207.253.146 - - [22/Jul/2021:07:45:55 +0000] "POST / HTTP/1.1" 404 196 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36"
2021-07-22T07:49:31.689000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:49:31.689000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET /icons/apache_pb2.gif HTTP/1.1" 200 4234 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
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If you would like to watch the logs in real time like tail -f, add the following option. aws logs tail --follow <Log Group>

$ aws logs tail --follow access_log
2021-07-22T07:45:55.422000+00:00 wordpress1 18.207.253.146 - - [22/Jul/2021:07:45:54 +0000] "GET /.env HTTP/1.1" 404 196 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36"
2021-07-22T07:45:59.986000+00:00 wordpress1 18.207.253.146 - - [22/Jul/2021:07:45:55 +0000] "POST / HTTP/1.1" 404 196 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.129 Safari/537.36"
2021-07-22T07:49:31.689000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:49:31.689000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET /icons/apache_pb2.gif HTTP/1.1" 200 4234 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:49:31.940000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET /icons/poweredby.png HTTP/1.1" 200 3412 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:49:33.195000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:31 +0000] "GET /favicon.ico HTTP/1.1" 404 196 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:49:34.198000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:33 +0000] "GET / HTTP/1.1" 403 4890 "https://www.google.com/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36"
2021-07-22T07:49:34.198000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:34 +0000] "GET /icons/poweredby.png HTTP/1.1" 200 3412 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36"
2021-07-22T07:49:38.949000+00:00 wordpress2 27.121.46.196 - - [22/Jul/2021:07:49:34 +0000] "GET /icons/apache_pb2.gif HTTP/1.1" 200 4234 "http://13.231.136.114/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.77 Safari/537.36"
2021-07-22T07:54:52.911000+00:00 wordpress1 27.121.46.196 - - [22/Jul/2021:07:54:52 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
2021-07-22T07:54:52.911000+00:00 wordpress1 27.121.46.196 - - [22/Jul/2021:07:54:52 +0000] "GET /icons/apache_pb2.gif HTTP/1.1" 200 4234 "http://54.168.233.33/" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
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The output describes this.

Timestamp + time zone streams messages

It is useful that I can watch logs in real time to use tail -f, but I cannot specify each streams, and the access logs of multiple servers are mixed together.

I will share cw which solves this problem.

What's cw?

cw is the best way to tail AWS CloudWatch Logs from your terminal. https://github.com/lucagrulla/cw

cw is a native executable targeting your OS, and not needed external dependencies such as pip and npm. Compared to awslogs which is famous helpful tool for CloudWatch Logs1, cw is written in golang and faster.

Moreover, it is very helpful that is possible to specify multiple groups. To use cw, I will try to execute tail -f for each streams, and watch logs.

Installation

You can install cw with brew command easily.

brew tap lucagrulla/tap
brew install cw
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Usage

If you have installed the AWS CLI locally, you have probably used registered your credentials to your local machine with aws configure, but if you have used aws cli within an EC2 instance with an IAM role, you will need to set the default region information in the file ~/.aws/config.

[default]
region = ap-northeast-1
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First, command cw -h.

$ cw -h
Usage: cw <command>

The best way to tail AWS Cloudwatch Logs from your terminal.

Flags:
  -h, --help               Show context-sensitive help.
      --endpoint=URL       The target AWS endpoint url. By default cw will use the default aws endpoints. NOTE: v4.0.0
                           dropped the flag short version.
      --profile=PROFILE    The target AWS profile. By default cw will use the default profile defined in the
                           .aws/credentials file. NOTE: v4.0.0 dropped the flag short version.
      --region=REGION      The target AWS region. By default cw will use the default region defined in the
                           .aws/credentials file. NOTE: v4.0.0 dropped the flag short version.
      --no-color           Disable coloured output.NOTE: v4.0.0 dropped the flag short version.
      --version            Print version information and quit

Commands:
  ls groups
    Show all groups.

  ls streams <group>
    Show all streams in a given log group.

  tail <groupName[:logStreamPrefix]> ...
    Tail log groups/streams.

Run "cw <command> --help" for more information on a command.
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There is the introduction of basically how to use and sub command. Next, command cw ls groups and you see list of Log groups collected CloudWatch Logs.

$ cw ls groups
/aws/lambda/Yuta-rds-auto-stop
/ecs/first-run-task-definition
RDSOSMetrics
access_log
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Command cw tail -f to watch CloudWatch Logs in real time.

$ cw tail access_log --follow --stream-name
wordpress2 - 27.121.46.196 - - [22/Jul/2021:09:19:33 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress2 - 27.121.46.196 - - [22/Jul/2021:09:20:24 +0000] "-" 408 - "-" "-"
wordpress2 - 27.121.46.196 - - [22/Jul/2021:09:20:29 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress2 - 27.121.46.196 - - [22/Jul/2021:09:20:29 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:20:48 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:20:49 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:20:49 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
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I can do that like tail -f. The main theme is that watching logs for each streams. You add option :stream after group.

$ cw tail access_log:wordpress1 --follow --stream-name
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:24:53 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:24:53 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:24:54 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:24:54 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:24:55 +0000] "GET / HTTP/1.1" 403 4890 "-" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
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The stream, wordpress1 is only displayed.

Unresolved

I continue to output logs for a while, an error suddenly occurs and the program terminates. An error occurs a few minutes after command execution.

....

wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:29:45 +0000] "GET /wordpress/wp-admin/plugin-install.php?tab=popular HTTP/1.1" 200 126481 "http://54.168.233.33/wordpress/wp-admin/plugin-install.php" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
wordpress1 - 27.121.46.196 - - [22/Jul/2021:09:29:47 +0000] "GET /wordpress/wp-admin/plugin-install.php?tab=recommended HTTP/1.1" 200 127412 "http://54.168.233.33/wordpress/wp-admin/plugin-install.php?tab=popular" "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.164 Safari/537.36"
operation error CloudWatch Logs: FilterLogEvents, exceeded maximum number of attempts, 3, https response error StatusCode: 400, RequestID: 69b981bb-0bcf-4263-951e-73aabf9ab379, api error ThrottlingException: Rate exceeded
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According to message, it is the API error that said The maximum number of attempts has been exceeded.

I don't know details, so I have a issue for developer. https://github.com/lucagrulla/cw/issues/214

Conclusion

The tool, cw is fast and useful. The error you saw made me bothered. I have a issue about that, but if someone has an idea, please submit a Pull Request.

Original

https://zenn.dev/yuta28/articles/cloudwatch-fast-tail

  1. https://github.com/jorgebastida/awslogs ↩

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