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Short Description
marathon-lb
Full Description

marathon-lb

Marathon-lb is a tool for managing HAProxy, by consuming Marathon's app state.

Features

  • Stateless design: no direct dependency on any third-party state store like ZooKeeper or etcd (except through Marathon)
  • Real-time LB updates, via Marathon's event bus
  • Support for Marathon's health checks
  • Multi-cert TLS/SSL support
  • Per-service HAProxy templates
  • DCOS integration
  • Automated Docker image builds (mesosphere/marathon-lb)
  • Global HAProxy templates which can be supplied at launch
  • Supports IP-per-task integration, such as Project Calico

Getting started

Take a look at the marathon-lb wiki for example usage, templates, and more.

Architecture

The marathon-lb script marathon_lb.py connects to the marathon API
to retrieve all running apps, generates a HAProxy config and reloads HAProxy.
By default, marathon-lb binds to the service port of every application and
sends incoming requests to the application instances.

Services are exposed on their service port (see
Service Discovery & Load Balancing
for reference) as defined in their Marathon definition. Furthermore, apps are
only exposed on LBs which have the same LB tag (or group) as defined in the Marathon
app's labels (using HAPROXY_GROUP). HAProxy parameters can be tuned by specify labels in your app.

To create a virtual host or hosts the HAPROXY_{n}_VHOST label needs to be set on the
given application. Applications with a vhost set will be exposed on ports 80
and 443, in addition to their service port. Multiple virtual hosts may be specified
in HAPROXY_{n}_VHOST using a comma as a delimiter between hostnames.

All applications are also exposed on port 9091, using the X-Marathon-App-Id
HTTP header. See the documentation for HAPROXY_HTTP_FRONTEND_APPID_HEAD in
the templates section

You can access the HAProxy statistics via :9090/haproxy?stats, and you can
retrieve the current HAProxy config from the :9090/_haproxy_getconfig endpoint.

Deployment

The package is currently available from the universe.
To deploy marathon-lb on the public slaves in your DCOS cluster,
simply run:

dcos package install marathon-lb

To configure a custom ssl-certificate, set the dcos cli option ssl-cert
to your concatenated cert and private key in .pem format. For more details
see the HAProxy documentation).

For further customization, templates can be added by pointing the dcos cli
option template-url to a tarball containing a directory templates/.
See comments in script on how to name those.

Docker

Synopsis: docker run -e PORTS=$portnumber --net=host mesosphere/marathon-lb sse|event|poll ...

You must set PORTS environment variable to allow haproxy bind to this port.
Syntax: docker run -e PORTS=9090 mesosphere/marathon-lb sse [other args]

You can pass in your own certificates for the SSL frontend by setting
the HAPROXY_SSL_CERT environment variable.

sse mode

In SSE mode, the script connects to the marathon events endpoint to get
notified about state changes. This only works with Marathon 0.11.0 or
newer versions.

Syntax: docker run mesosphere/marathon-lb sse [other args]

event mode

In event mode, the script registers a HTTP callback in marathon to get
notified when state changes.

Syntax: docker run mesosphere/marathon-lb event callback-addr:port [other args]

poll mode

If you can't use the HTTP callbacks, the script can poll the APIs to get
the schedulers state periodically.

Syntax: docker run mesosphere/marathon-lb poll [other args]

To change the poll interval (defaults to 60s), you can set the POLL_INTERVAL
environment variable.

Direct invocation

You can also run the update script directly.
To generate an HAProxy configuration from Marathon running at localhost:8080 with the marathon_lb.py script, run:

$ ./marathon_lb.py --marathon http://localhost:8080 --group external

It is possible to pass --auth-credentials= option if your Marathon requires authentication:

$ ./marathon_lb.py --marathon http://localhost:8080 --auth-credentials=admin:password

This will refresh haproxy.cfg, and if there were any changes, then it will
automatically reload HAProxy. Only apps with the label HAPROXY_GROUP=external
will be exposed on this LB.

marathon_lb.py has a lot of additional functionality like sticky sessions, HTTP to HTTPS redirection, SSL offloading, virtual host support and templating capabilities.

To get the full documentation run:

$ ./marathon_lb.py --help

Providing SSL certificates

You can provide your SSL certificate paths to be placed in frontend marathon_https_in section with --ssl-certs.

$ ./marathon_lb.py --marathon http://localhost:8080 --group external --ssl-certs /etc/ssl/site1.co,/etc/ssl/site2.co

If you are using the script directly, you have two options:

  • Provide nothing and config will use /etc/ssl/mesosphere.com.pem as the certificate path. Put the certificate in this path or edit the file for the correct path.
  • Provide --ssl-certs command line argument and config will use these paths.

If you are using the provided run script or Docker image, you have three options:

  • Provide your certificate text in HAPROXY_SSL_CERT environment variable. Contents will be written to /etc/ssl/mesosphere.com.pem. Config will use this path unless you specified extra certificate paths as in the next option.
  • Provide SSL certificate paths with --ssl-certs command line argument. Your config will use these certificate paths.
  • Provide nothing and it will create self-signed certificate on /etc/ssl/mesosphere.com.pem and config will use it.

Skipping configuration validation

You can skip the configuration file validation (via calling HAProxy service) process if you don't have HAProxy installed. This is especially useful if you are running HAProxy on Docker containers.

$ ./marathon_lb.py --marathon http://localhost:8080 --group external --skip-validation

API endpoints

Marathon-lb exposes a few endpoints on port 9090 (by default). They are:

Endpoint Description
:9090/haproxy?stats HAProxy stats endpoint. This produces an HTML page which can be viewed in your browser, providing various statistics about the current HAProxy instance.
:9090/haproxy?stats;csv This is a CSV version of the stats above, which can be consumed by other tools. For example, it's used in the bluegreen_deploy.py script.
:9090/_haproxy_health_check HAProxy health check endpoint. Returns 200 OK if HAProxy is healthy.
:9090/_haproxy_getconfig Returns the HAProxy config file as it was when HAProxy was started. Implemented in getconfig.lua.
:9090/_haproxy_getpids Returns the PIDs for all HAProxy instances within the current process namespace. This literally returns $(pidof haproxy). Implemented in getpids.lua. This is also used by the bluegreen_deploy.py script to determine if connections have finished draining during a deploy.

HAProxy configuration

App labels

App labels are specified in the Marathon app definition. These can be used to override HAProxy behaviour. For example, to specify the external group for an app with a virtual host named service.mesosphere.com:

{
  "id": "http-service",
  "labels": {
    "HAPROXY_GROUP":"external",
    "HAPROXY_0_VHOST":"service.mesosphere.com"
  }
}

Some labels are specified per service port. These are denoted with the {n} parameter in the label key, where {n} corresponds to the service port index, beginning at 0.

See the configuration doc for the full list
of labels.

Templates

Marathon-lb searches for configuration files in the templates/
directory. The templates/ directory is located in a relative
path from where the script is run. Some templates can also be
overridden per app service port. You may add your
own templates to the Docker image, or provide them at startup.

See the configuration doc for the full list
of templates.

Overridable templates

Some templates may be overridden using app labels,
as per the labels section. Strings are interpreted as literal
HAProxy configuration parameters, with substitutions respected (as per the
templates section). The HAProxy configuration will be validated
for correctness before reloading HAProxy after changes. Note: Since the
HAProxy config is checked before reloading, if an app's HAProxy
labels aren't syntactically correct, HAProxy will not be reloaded and may
result in stale config.

Here is an example for a service called http-service which requires that
http-keep-alive be disabled:

{
  "id": "http-service",
  "labels":{
    "HAPROXY_GROUP":"external",
    "HAPROXY_0_BACKEND_HTTP_OPTIONS":"  option forwardfor\n  no option http-keep-alive\n  http-request set-header X-Forwarded-Port %[dst_port]\n  http-request add-header X-Forwarded-Proto https if { ssl_fc }\n"
  }
}

The full list of per service port templates which can be specified
are documented here.

Zero downtime deployments

Marathon-lb is able to perform canary style blue/green deployment with zero downtime. To execute such deployments, you must follow certain patterns when using Marathon.

The deployment method is described in this Marathon document. Marathon-lb provides an implementation of the aforementioned deployment method with the script bluegreen_deploy.py. To perform a zero downtime deploy using bluegreen_deploy.py, you must:

  • Specify the HAPROXY_DEPLOYMENT_GROUP and HAPROXY_DEPLOYMENT_ALT_PORT labels in your app template
    • HAPROXY_DEPLOYMENT_GROUP: This label uniquely identifies a pair of apps belonging to a blue/green deployment, and will be used as the app name in the HAProxy configuration
    • HAPROXY_DEPLOYMENT_ALT_PORT: An alternate service port is required because Marathon requires service ports to be unique across all apps
  • Only use 1 service port: multiple ports are not yet implemented
  • Use the provided bluegreen_deploy.py script to orchestrate the deploy: the script will make API calls to Marathon, and use the HAProxy stats endpoint to gracefully terminate instances
  • The marathon-lb container must be run in privileged mode (to execute iptables commands) due to the issues outlined in the excellent blog post by the Yelp engineering team found here
  • If you have long-lived TCP connections using the same HAProxy instances, it may cause the deploy to take longer than necessary. The script will wait up to 5 minutes (by default) for connections to drain from HAProxy between steps, but any long-lived TCP connections will cause old instances of HAProxy to stick around.

An example minimal configuration for a test instance of nginx is included here. You might execute a deployment from a CI tool like Jenkins with:

./bluegreen_deploy.py -j 1-nginx.json -m http://master.mesos:8080 -f -l http://marathon-lb.marathon.mesos:9090 --syslog-socket /dev/null

Zero downtime deployments are accomplished through the use of a Lua module, which reports the number of HAProxy processes which are currently running by hitting the stats endpoint at the /_haproxy_getpids. After a restart, there will be multiple HAProxy PIDs until all remaining connections have gracefully terminated. By waiting for all connections to complete, you may safely and deterministically drain tasks. A caveat of this, however, is that if you have any long-lived connections on the same LB, HAProxy will continue to run and serve those connections until they complete, thereby breaking this technique.

Mesos with IP-per-task support

Marathon-lb supports load balancing for applications that use the Mesos IP-per-task
feature, whereby each task is assigned unique, accessible, IP addresses. For these
tasks services are directly accessible via the configured discovery ports and there
is no host port mapping. Note, that due to limitations with Marathon (see
mesosphere/marathon#3636)
configured service ports are not exposed to marathon-lb for IP-per-task apps.

For these apps, if the service ports are missing from the Marathon app data,
marathon-lb will automatically assign port values from a configurable range. The range
is configured using the --min-serv-port-ip-per-task and --max-serv-port-ip-per-task
options. While port assignment is deterministic, the assignment is not guaranteed if
you change the current set of deployed apps. In other words, when you deploy a new
app, the port assignments may change.

Contributing

PRs are welcome, but here are a few general guidelines:

  • Avoid making changes which may break existing behaviour
  • Document new features
  • Update/include tests for new functionality
  • Use the pre-commit hook to automatically generate docs:
    bash /path/to/marathon-lb/scripts/install-git-hooks.sh
    
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zazrivec
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