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https://github.com/lyft/metadataproxy

A proxy for AWS's metadata service that gives out scoped IAM credentials from STS
https://github.com/lyft/metadataproxy

lyft

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A proxy for AWS's metadata service that gives out scoped IAM credentials from STS

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README 

        
# metadataproxy



The metadataproxy is used to allow containers to acquire IAM roles. By metadata we mean [EC2 instance meta data](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-metadata.html) which is normally available to EC2 instances. This proxy exposes the meta data to containers inside or outside of EC2 hosts, allowing you to provide scoped IAM roles to individual containers, rather than giving them the full IAM permissions of an IAM role or IAM user.



## Installation



From inside of the repo run the following commands:



```bash

mkdir -p /srv/metadataproxy

cd /srv/metadataproxy

virtualenv venv

source venv/bin/activate

pip install metadataproxy

deactivate

```



## Configuration



### Modes of operation



See [the settings file](https://github.com/lyft/metadataproxy/blob/master/metadataproxy/settings.py)

for specific configuration options.



The metadataproxy has two basic modes of operation:



1. Running in AWS where it simply proxies most routes to the real metadata

   service.

2. Running outside of AWS where it mocks out most routes.



To enable mocking, use the environment variable:



```

export MOCK_API=true

```



### AWS credentials



metadataproxy relies on boto configuration for its AWS credentials. If metadata

IAM credentials are available, it will use this. Otherwise, you'll need to use

.aws/credentials, .boto, or environment variables to specify the IAM

credentials before the service is started.



### Role assumption



For IAM routes, the metadataproxy will use STS to assume roles for containers.

To do so it takes the incoming IP address of metadata requests and finds the

running docker container associated with the IP address. It uses the value of

the container's `IAM_ROLE` environment variable as the role it will assume. It

then assumes the role and gives back STS credentials in the metadata response.



STS-attained credentials are cached and automatically rotated as they expire.



#### Container-specific roles



To specify the role of a container, simply launch it with the `IAM_ROLE`

environment variable set to the IAM role you wish the container to run with.



If the trust policy for the role requires an ExternalId, you can set this

using the `IAM_EXTERNAL_ID` environment variable. This is most frequently

used with cross-account role access scenarios. For more information on

when you should use an External ID for your roles, see:



http://docs.aws.amazon.com/IAM/latest/UserGuide/id_roles_create_for-user_externalid.html



```shell

docker run -e IAM_ROLE=my-role ubuntu:14.04

docker run -e IAM_ROLE=their-role@another-account -e IAM_EXTERNAL_ID=random-unique-string ubuntu:14.04

```



#### Configurable Behavior



There are a number of environment variables that can be set to tune

metadata proxy's behavior. They can either be exported by the start

script, or set via docker environment variables.



| Variable | Type | Default | Description |

| -------- | ---- | ------- | ----------- |

| **DEFAULT\_ROLE** | String | | Role to use if IAM\_ROLE is not set in a container's environment. If unset the container will get no IAM credentials. |

| **DEFAULT\_ACCOUNT\_ID** | String | | The default account ID to assume roles in, if IAM\_ROLE does not contain account information. If unset, metadataproxy will attempt to lookup role ARNs using iam:GetRole. |

| **ROLE\_SESSION\_KEY** | String | | Optional key in container labels or environment variables to use for role session name. Prefix with `Labels:` or `Env:` respectively to indicate where key should be found. Useful to pass through metadata such as a CI job ID or launching user for audit purposes, as the role session name is included in the ARN that appears in access logs. |

| DEBUG | Boolean | False | Enable debug mode. You should not do this in production as it will leak IAM credentials into your logs |

| DOCKER\_URL | String | unix://var/run/docker.sock | Url of the docker daemon. The default is to access docker via its socket. |

| METADATA\_URL | String | http://169.254.169.254 | URL of the metadata service. Default is the normal location of the metadata service in AWS. |

| MOCK\_API | Boolean | False | Whether or not to mock all metadata endpoints. If True, mocked data will be returned to callers. If False, all endpoints except for IAM endpoints will be proxied through to the real metadata service. |

| MOCKED\_INSTANCE\_ID | String | mockedid | When mocking the API, use the following instance id in returned data. |

| AWS\_ACCOUNT\_MAP | JSON String | `{}` | A mapping of account names to account IDs. This allows you to use user-friendly names instead of account IDs in IAM\_ROLE environment variable values. |

| AWS\_REGION | String |  | AWS Region for the STS endpoint allow you to call region based endpoint instead of global one. [AWS STS region endpoints.](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_credentials_temp_enable-regions.html#id_credentials_region-endpoints) |

| ROLE\_EXPIRATION\_THRESHOLD | Integer | 15 | The threshold before credentials expire in minutes at which metadataproxy will attempt to load new credentials. |

| ROLE\_MAPPING\_FILE | Path String | | A json file that has a dict mapping of IP addresses to role names. Can be used if docker networking has been disabled and you are managing IP addressing for containers through another process. |

| ROLE\_REVERSE\_LOOKUP | Boolean | False | Enable performing a reverse lookup of incoming IP addresses to match containers by hostname. Useful if you've disabled networking in docker, but set hostnames for containers in /etc/hosts or DNS. |

| HOSTNAME\_MATCH\_REGEX | Regex String | `^.*$` | Limit reverse lookup container matching to hostnames that match the specified pattern. |

| PATCH_ECS_ALLOWED_HOSTS | String | | Patch botocore's allowed hosts for ContainerMetadataFetcher to support aws-vault's --ecs-server option. This will inject the provided host into the allowed addresses botocore will allow for the AWS_CONTAINER_CREDENTIALS_FULL_URI environment. |



#### Default Roles



When no role is matched, `metadataproxy` will use the role specified in the 

`DEFAULT_ROLE` `metadataproxy` environment variable. If no DEFAULT\_ROLE is

specified as a fallback, then your docker container without an `IAM_ROLE`

environment variable will fail to retrieve credentials.



#### Role Formats



The following are all supported formats for specifying roles:



- By Role:



    ```shell

    IAM_ROLE=my-role

    ```



- By Role@AccountId



    ```shell

    IAM_ROLE=my-role@012345678910

    ```



- By ARN:



    ```shell

    IAM_ROLE=arn:aws:iam::012345678910:role/my-role

    ```



### Role structure



A useful way to deploy this metadataproxy is with a two-tier role

structure:



1.  The first tier is the EC2 service role for the instances running

    your containers.  Call it `DockerHostRole`.  Your instances must

    be launched with a policy that assigns this role.



2.  The second tier is the role that each container will use.  These

    roles must trust your own account ("Role for Cross-Account

    Access" in AWS terms).  Call it `ContainerRole1`.



3.  metadataproxy needs to query and assume the container role.  So

    the `DockerHostRole` policy must permit this for each container

    role.  For example:

    ```

    "Statement": [ {

        "Effect": "Allow",

        "Action": [

            "iam:GetRole",

            "sts:AssumeRole"

        ],

        "Resource": [

            "arn:aws:iam::012345678901:role/ContainerRole1",

            "arn:aws:iam::012345678901:role/ContainerRole2"

        ]

    } ]

    ```



4. Now customize `ContainerRole1` & friends as you like



Note: The `ContainerRole1` role should have a trust relationship that allows it to be assumed by the `user` which is associated to the host machine running the `sts:AssumeRole` command.  An example trust relationship for `ContainRole1` may look like:



```

{

  "Version": "2012-10-17",

  "Statement": [

    {

      "Effect": "Allow",

      "Principal": {

        "AWS": "arn:aws:iam::012345678901:root",

        "Service": "ec2.amazonaws.com"

      },

      "Action": "sts:AssumeRole"

    }

  ]

}

```



### Routing container traffic to metadataproxy



Using iptables, we can forward traffic meant to 169.254.169.254 from docker0 to

the metadataproxy. The following example assumes the metadataproxy is run on

the host, and not in a container:



```

/sbin/iptables \

  --append PREROUTING \

  --destination 169.254.169.254 \

  --protocol tcp \

  --dport 80 \

  --in-interface docker0 \

  --jump DNAT \

  --table nat \

  --to-destination 127.0.0.1:8000 \

  --wait

```



If you'd like to start the metadataproxy in a container, it's recommended to

use host-only networking. Also, it's necessary to volume mount in the docker

socket, as metadataproxy must be able to interact with docker.



Be aware that non-host-mode containers will not be able to contact

127.0.0.1 in the host network stack.  As an alternative, you can use

the meta-data service to find the local address.  In this case, you

probably want to restrict proxy access to the docker0 interface!



```

LOCAL_IPV4=$(curl http://169.254.169.254/latest/meta-data/local-ipv4)



/sbin/iptables \

  --append PREROUTING \

  --destination 169.254.169.254 \

  --protocol tcp \

  --dport 80 \

  --in-interface docker0 \

  --jump DNAT \

  --table nat \

  --to-destination $LOCAL_IPV4:8000 \

  --wait



/sbin/iptables \

  --wait \

  --insert INPUT 1 \

  --protocol tcp \

  --dport 80 \

  \! \

  --in-interface docker0 \

  --jump DROP

```



## Run metadataproxy without docker



In the following we assume \_my\_config\_ is a bash file with exports for all of

the necessary settings discussed in the configuration section.



```

source my_config

cd /srv/metadataproxy

source venv/bin/activate

gunicorn metadataproxy:app --workers=2 -k gevent

```



## Run metadataproxy with docker



For production purposes, you'll want to kick up a container to run.

You can build one with the included Dockerfile.  To run, do something like:

```bash

docker run --net=host \

    -v /var/run/docker.sock:/var/run/docker.sock \

    lyft/metadataproxy

```



### gunicorn settings



The following environment variables can be set to configure gunicorn (defaults

are set in the examples):



```

# Change the IP address the gunicorn worker is listening on. You likely want to

# leave this as the default

HOST=0.0.0.0



# Change the port the gunicorn worker is listening on.

PORT=8000



# Change the number of worker processes gunicorn will run with. The default is

# 1, which is likely enough since metadataproxy is using gevent and its work is

# completely IO bound. Increasing the number of workers will likely make your

# in-memory cache less efficient

WORKERS=1



# Enable debug mode (you should not do this in production as it will leak IAM

# credentials into your logs)

DEBUG=False

```



## Contributing



### Code of conduct



This project is governed by [Lyft's code of

conduct](https://github.com/lyft/code-of-conduct).

All contributors and participants agree to abide by its terms.



### Sign the Contributor License Agreement (CLA)



We require a CLA for code contributions, so before we can accept a pull request

we need to have a signed CLA. Please [visit our CLA

service](https://oss.lyft.com/cla)

follow the instructions to sign the CLA.



### File issues in Github



In general all enhancements or bugs should be tracked via github issues before

PRs are submitted. We don't require them, but it'll help us plan and track.



When submitting bugs through issues, please try to be as descriptive as

possible. It'll make it easier and quicker for everyone if the developers can

easily reproduce your bug.



### Submit pull requests



Our only method of accepting code changes is through github pull requests.