About

Gor is a simple http traffic replication tool written in Go. Its main goal is to replay traffic from production servers to staging and dev environments.

Now you can test your code on real user sessions in an automated and repeatable fashion. No more falling down in production!

Here is basic workflow: The listener server catches http traffic and sends it to the replay server or saves to file.The replay server forwards traffic to a given address.

Examples

Capture traffic from port

# Run on servers where you want to catch traffic. You can run it on each `web` machine.
sudo gor --input-raw :80 --output-tcp replay.local:28020

# Replay server (replay.local).
gor --input-tcp replay.local:28020 --output-http http://staging.com

Using 1 Gor instance for both listening and replaying

It's recommended to use separate server for replaying traffic, but if you have enough CPU resources you can use single Gor instance.

sudo gor --input-raw :80 --output-http "http://staging.com"

Advanced use

Rate limiting

Both replay and listener support rate limiting. It can be useful if you want forward only part of production traffic and not overload your staging environment. You can specify your desired requests per second using the "|" operator after the server address:

Limiting replay

# staging.server will not get more than 10 requests per second
gor --input-tcp :28020 --output-http "http://staging.com|10"

Limiting listener

# replay server will not get more than 10 requests per second
# useful for high-load environments
gor --input-raw :80 --output-tcp "replay.local:28020|10"

Match on regexp of url

# only forward requests being sent to the api... domains
gor --input-raw :8080 --output-http staging.com --output-http-url-regexp ^www.

Filter based on regexp of header

# only forward requests with an api version of 1.0x
gor --input-raw :8080 --output-http staging.com --output-http-header-filter api-version:^1\.0\d

Filter based on hash of header

# send 1/32 of all users consistently to staging
gor --input-raw :8080 --output-http staging.com --output-http-header-hash-filter user-id:1/32

Forward to multiple addresses

You can forward traffic to multiple endpoints. Just add multiple --output-* arguments.

gor --input-tcp :28020 --output-http "http://staging.com"  --output-http "http://dev.com"

Splitting traffic

By default it will send same traffic to all outputs, but you have options to equally split it:

gor --input-tcp :28020 --output-http "http://staging.com"  --output-http "http://dev.com" --split-output true

Saving requests to file

You can save requests to file, and replay them later:

# write to file
gor --input-raw :80 --output-file requests.gor

# read from file
gor --input-file requests.gor --output-http "http://staging.com"

Note: Replay will preserve the original time differences between requests.

Injecting headers

Additional headers can be injected/overwritten into requests during replay. This may be useful if you need to identify requests generated by Gor or enable feature flagged functionality in an application:

gor --input-raw :80 --output-http "http://staging.server" \
    --output-http-header "User-Agent: Replayed by Gor" \
    --output-http-header "Enable-Feature-X: true"

Filtering HTTP methods

Requests not matching a specified whitelist can be filtered out. For example to strip non-nullipotent requests:

gor --input-raw :80 --output-http "http://staging.server" \
    --output-http-method GET \
    --output-http-method OPTIONS

Basic Auth

If your development or staging environment is protected by Basic Authentication then those credentials can be injected in during the replay:

gor --input-raw :80 --output-http "http://user:pass@staging .com"

Note: This will overwrite any Authorization headers in the original request.

Additional help

Feel free to ask question directly by email or by creating github issue.

Latest releases (including binaries)

https://github.com/buger/gor/releases

Command line reference

gor -h output:

  -cpuprofile="": write cpu profile to file
  -memprofile="": write memory profile to this file
  
  -input-dummy=[]: Used for testing outputs. Emits 'Get /' request every 1s

  -input-file=[]: Read requests from file: 
    gor --input-file ./requests.gor --output-http staging.com

  -input-raw=[]: Capture traffic from given port (use RAW sockets and require *sudo* access):
    # Capture traffic from 8080 port
    gor --input-raw :8080 --output-http staging.com

  -input-tcp=[]: Used for internal communication between Gor instances. Example: 
    # Receive requests from other Gor instances on 28020 port, and redirect output to staging
    gor --input-tcp :28020 --output-http staging.com

  -output-dummy=[]: Used for testing inputs. Just prints data coming from inputs.

  -output-file=[]: Write incoming requests to file: 
    gor --input-raw :80 --output-file ./requests.gor

  -output-http=[]: Forwards incoming requests to given http address.
    # Redirect all incoming requests to staging.com address 
    gor --input-raw :80 --output-http http://staging.com

  -output-http-header=[]: Inject additional headers to http reqest:
    gor --input-raw :8080 --output-http staging.com --output-http-header 'User-Agent: Gor'

  -output-http-header-filter=[]: A regexp to match a specific header against. Requests with non-matching headers will be dropped:
    gor --input-raw :8080 --output-http staging.com --output-http-header-filter api-version:^v1

  -output-http-header-hash-filter=[]: Takes a fraction of requests, consistently taking or rejecting a request based on the FNV32-1A hash of a specific header. The fraction must have a denominator that is a power of two:
    gor --input-raw :8080 --output-http staging.com --output-http-header-hash-filter user-id:1/4

  -output-http-url-regexp=: A regexp to match requests against. Anything else will be dropped:
    gor --input-raw :8080 --output-http staging.com --output-http-url-regexp ^www.
    
  -output-tcp=[]: Used for internal communication between Gor instances. Example: 
    # Listen for requests on 80 port and forward them to other Gor instance on 28020 port
    gor --input-raw :80 --output-tcp replay.local:28020
    
  -split-output=false: By default each output gets same traffic. If set to `true` it splits traffic equally among all outputs.

Building from source

1. Setup standard Go environment http://golang.org/doc/code.html and ensure that $GOPATH environment variable properly set.
2. go get github.com/buger/gor.
3. cd $GOPATH/src/github.com/buger/gor
4. go build to get binary, or go test to run tests

FAQ

What OS are supported?

For now only Linux based. *BSD (including MacOS is not supported yet, check buger#22 for details)

Why does the --input-raw requires sudo or root access?

Listener works by sniffing traffic from a given port. It's accessible only by using sudo or root access.

I'm getting 'too many open files' error

Typical linux shell has a small open files soft limit at 1024. You can easily raise that when you do this before starting your gor replay process:

ulimit -n 64000

More about ulimit: http://blog.thecodingmachine.com/content/solving-too-many-open-files-exception-red5-or-any-other-application

Tuning

To achieve the top most performance you should tune the source server system limits:

net.ipv4.tcp_max_tw_buckets = 65536
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 0
net.ipv4.tcp_max_syn_backlog = 131072
net.ipv4.tcp_syn_retries = 3
net.ipv4.tcp_synack_retries = 3
net.ipv4.tcp_retries1 = 3
net.ipv4.tcp_retries2 = 8
net.ipv4.tcp_rmem = 16384 174760 349520
net.ipv4.tcp_wmem = 16384 131072 262144
net.ipv4.tcp_mem = 262144 524288 1048576
net.ipv4.tcp_max_orphans = 65536
net.ipv4.tcp_fin_timeout = 10
net.ipv4.tcp_low_latency = 1
net.ipv4.tcp_syncookies = 0

Contributing

1. Fork it
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Added some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create new Pull Request

Companies using Gor

• http://granify.com
• GOV.UK (Government Digital Service)
• To add your company drop me a line to github.com/buger or leonsbox@gmail.com