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Get ECS service info (e.g. EC2 instance id) by a given service name.

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aws_ecs_services

Why

I would like to easily ssh into the instance an ECS service is running on. When deployed into a cluster with several instances you cannot accomplish this using awscli.

I work through a VPN, so I am only interested in the instances' private IP addresses. When using the AWS Session Manager I am interested in the instances' ids.

The script provides two ways to get the instance's information:

  • 1. approach: For ECS services that use service discovery and register a DNS name with AWS Route53, it's possible to get the services's/container's private IP and then check which EC2 instance contains the same private IP.
  • 2. approach: When using AWS SSM (with ssm-agent on EC2 instances and AWS Session Manager Plugin locally) the tool will connect to every ECS cluster instance and compares a given service with running ones (running docker containers).
  • 3. approach: This approach does not require a special setup. The tool just goes through the list of AWS ECS tasks (task deifnitions) in the cluster and compares a given task with ative task definitions.

In case the infrastructure is deployed with terraform, the ECS service and tasks names as well as the DNS names of the services become predictable.

There are other commands, see below.

How

The tool is best used with aws-vault. So far I did not implement reading AWS profiles with boto3 e.g.

1. approach (services with service discovery only) using by-service-dns:

aws_ecs_services by-service-dns --region <aws_region> --cluster <ecs_cluster_name> --dns <service_dns_name> [--output <output_info>]

Note:

  • It's also possible to use a configuration file (see below) in order to shorten the above command.

The tool requires the DNS name of the service (AWS Route53). It also requires the name of the cluster the service was created in. Also the tool requires the AWS region to use.

The association between the service's DNS name and the instance private IP:

  • Get the IP of the service by DNS name (host name).
    • IP is changing constantly (with every deployment), DNS name is not.
  • Get all the cluster instances.
    • Make sure you configure the correct cluster (The service nneds to be located in there.).
  • Get the private IP addresses of these instances and compareto the IP address of the service.
  • The match reveals the correct instance.

2. approach (all services, requires a working AWS SSM setup) using by-service-name:

aws_ecs_services by-service-name --region <aws_region> --cluster <ecs_cluster_name> --name <part_of_service_name_even_regex>

Note:

  • It's also possible to use a configuration file (see below) in order to shorten the above command.

The tool requires the name of the service (AWS ECS service) or part of it (regular expressions allowed). It also requires the name of the cluster the service was created in. Also the tool requires the AWS region to work in.

All cluster instances are checked for running docker containers. Using regular expressions the given service name is searched for in the list of docker container names. If a match is found the according instance id will be returned.

Only the first match will be considered.

3. approach (all services) using by-task-name:

aws_ecs_services by-task-name --region <aws_region> --cluster <ecs_cluster_name> --name <part_of_task_name_even_regex>

Note:

  • It's also possible to use a configuration file (see below) in order to shorten the above command.

The tool requires the name of the service (AWS ECS task definition) or part of it (regular expressions allowed). It also requires the name of the cluster the task defintion is active in. Also the tool requires the AWS region to work in.

All cluster tasks are checked. Using regular expressions the given task name is searched for in the list of cluster tasks. If a match is found the according instance id will be returned.

Only the first match will be considered.

Usage

For better readability I will leave out aws-vault in the examples below.

These are the possible commands:

  • by-service-dns - Get instance information by service's dns name.
  • by-service-name - Get instance id by service's name.
  • by-task-name - Get instance id by task definition name.
  • list-clusters - Get all clusters.
  • list-instances - Get all cluster instances (instance ids).
  • list-ec2-instances - In case the ecs-agent is not connected, it gets all possible EC2 instance ids and private IP addresses.
  • list-services - Get all active cluster services.
  • list-tasks - Get all active cluster tasks.
  • list-configured-services - Get all configured services, in the config file. Requires a config file.
  • list-configured-projects - Get all configured projects, in the config file. Requires a config file.

Here you can find some examples to ssh into the appropriate EC2 instance:

# Get instance IP address by service DNS name
ssh ec2-user@"$(aws_ecs_services by-service-dns --region eu-west-2 --cluster my-cluster --dns dns.name.com)"
# Get instance ID by service DNS name
aws ssm start-session --target "$(aws_ecs_services by-service-dns --region eu-west-2 --cluster my-cluster --dns dns.name.com --output id)"
# Get instance ID by service name
aws ssm start-session --target "$(aws_ecs_services by-service-name --region eu-west-2 --cluster my-cluster --name part_of_service_name_even_regex)"

Note:

  • The configuration can be done within a configuration file as well (see Use with configuration file).

Here you can find further examples of how to use this tool:

# List all instance IDs in cluster
aws_ecs_services list-instances --region eu-west-2 --cluster my-cluster
# List all service names deployed in the cluster
aws_ecs_services list-services --region eu-west-2 --cluster my-cluster

Using regular expressions aws_ecs_services by-service-name --region eu-west-2 --cluster dev --name "price-redis-[a-z0-9]*$" --debug

Note:

  • --debug shows additional output in order to really get the correct container (service) in case more than one was found e.g..

The default output of the subcommand by-service-dns is the instance's private IP address.

  • If called with --output id it displays the instance's id.
        # Get instance id by service DNS name
        aws ssm start-session --target "$(aws_ecs_services by-service-dns --region eu-west-2 --cluster my-cluster --dns dns.name.com --output id)"
    
  • If called with --output all it displays both of the values above. In addition it returns the instance's private DNS name.
  • If called with --output service it displays the service's IP address only.

It's possible to define a configuration file (see Use with configuration file).

  • --project defines the project defined in the configuration file to be used.
  • --service defines the service for the given project defined in the configuration file to be used.

Use with configuration file

When using a configuration file most of the cli options can be left out.

The default location is ~/.config/aws_tools/config.

The configuration file template looks like this, also see ./config.template:

{
    "region": "eu-west-1",
    "projects": {
        "projectA": {
            "region": "eu-west-2",
            "cluster": "default",
            "dns": "{service}.domain.com",
            "services": {
                "serviceA": {
                    "description": "Service is using project-level default values for 'cluster' and 'dns'."
                },
                "serviceB": {
                    "description": "Service name is part of cluster name. Using variable replacement for 'cluster'",
                    "cluster": "{cluster}-serviceB"
                },
                "serviceC": {
                    "description": "Service name is part of cluster name. Using variable replacement for 'service'. Eventually same as with 'serviceB'.",
                    "cluster": "{cluster}-{service}"
                },
                "serviceD": {
                    "description": "Same as 'serviceC', even runs in the same AWS ECS service - Is configured as additional container in the task definition of 'serviceC'.",
                    "cluster": "{cluster}-serviceC",
                    "dns": "serviceC.domain.com"
                },
                "serviceE": {
                    "description": "Service is not deployed with 'awsvpc', no dedicated IP, no DNS name.",
                    "dns": ""
                }
            }
        },
        "projectB": {
            "cluster": "projectB",
            "dns": "{cluster}-{service}.domain.com",
            "services": {
                "serviceA": {
                    "description": "Service is using project-level default values for 'cluster' and 'dns'."
                }
            }
        }
    }
}

Note:

  • For the following examples the ./config.template configuration can be assumed.

There is a top-level region specified. Additionally, on project-level (for every configured project), you can set another region.

A project can also have a name for the cluster as well as a dns name, which is necessary when AWS ECS services are deployed with the awsvpc network mode and get their own IP address, register with AWS CloudMap and AWS Route53 etc.

To list all the configured projects:

    aws_ecs_services list-configured-projects
    # Result:
    projectA
    projectB

Each project has services.

To list all the configured services:

    # aws_ecs_services --project <configured_project> list-configured-services
    aws_ecs_services --project projectA list-configured-services
    # Result:
    serviceA
    serviceB
    serviceC
    serviceD
    serviceE

The service-level configuration for cluster and dns overrules the project-level configuration.

Example calls (see Usage for using cli options):

  • List instances in the cluster:
    • When using a config file: Right now, this only checks instances in the project-level cluster. service-level clusters are not considered, yet.
    • You can list instances using the cli options (see Usage).
    # aws_ecs_services --project <configured_project> list-instances
    aws_ecs_services --project projectA list-instances
    # Result is a string of AWS EC2 instance ids of instances in the cluster. Something like:
    i-04d153c42e9b71b8a i-05169fb090fb6a68b i-03029360ad379566d i-01b155c39d4324ad7
  • List running services in the cluster:
    • Actually lists the docker container names.
    • When using a config file: Right now, this only checks instances in the project-level cluster. service-level clusters are not considered, yet.
    • You can list running services using the cli options (see Usage).
    # aws_ecs_services --project <configured_project> list-services
    aws_ecs_services --project projectA list-services
    # Result is a list of AWS ECS services (docker container names) running in the cluster. Something like:
    ecs-default-serviceA-1-default-serviceA-b4cedd8899a7cba90b00
    ecs-deafult-serviceB-serviceB-1-default-serviceB-serviceB-b4cedd8899a7cba90b01
    ecs-default-serviceC-serviceC-1-default-serviceC-serviceC-b4cedd8899a7cba90b02
    ecs-default-serviceC-serviceD-1-default-serviceC-serviceD-b4cedd8899a7cba90b04
    ecs-default-serviceE-1-default-serviceE-b4cedd8899a7cba90b05
  • List running tasks in the cluster:
    • Actually lists the ECS task defintion names.
    • When using a config file: Right now, this only checks instances in the project-level cluster. service-level clusters are not considered, yet.
    • You can list running tasks using the cli options (see Usage).
    # aws_ecs_services --project <configured_project> list-tasks
    aws_ecs_services --project projectA list-tasks
    # Result is a list of AWS ECS tasks running in the cluster. Something like:
    arn:aws:ecs:eu-west-2:<account_id>:task-definition/serviceB:87
    arn:aws:ecs:eu-west-2:<account_id>:task-definition/serviceE:262
  • Get the instance for a service by its DNS name: by-service-dns:
    # aws_ecs_services --project <configured_project> --service <configured_service> by-service-dns --output id
    aws_ecs_services --project projectA --service serviceA by-service-dns --output id
    # Result:
    i-00epg17383ba1e1cg
  • Get the instance for a service by its ECS service name: by-service-name:
    • --service is used to search for the project's service in the configuration file.
    • By default --service is also used as the running AWS ECS service to search for.
    • It is possible to additionally add the --name option to by-service-name, which allows regular expressions. --name is preferred over the value of --service when it comes to searching for the running AWS ECS service (see Usage).
      • Use case: Different services where one service name is part of another one's name.
        • With services like serviceA and serviceA1, when running with --service serviceA it is possible that the ECS service serviceA1 is found instead.
        • This issue can be resolved by passing --service serviceA by-service-name --name "serviceA-[0-9]+".
        • Instead of --name you can also configure "name": "serviceA-[0-9]+" per service in the configuration file.
        • This makes sure to use service-level configuration for serviceA but specifies the AWS ECS service name to search for in greater detail.
    # aws_ecs_services --project <configured_project> --service <configured_service> by-service-name
    aws_ecs_services --project projectA --service serviceA by-service-name
    INFO:AwsGetInstance:Instance 'i-04ef6e335a618932a' runs container 'ecs-default-serviceA1-1-default-serviceA1-g6frgg3388d1hjb63f01'
    # Result:
    i-04ef6e335a618932a

    # aws_ecs_services --project <configured_project> --service <configured_service> by-service-name --name <part_of_service_name_even_regex>
    aws_ecs_services --project projectA --service serviceA by-service-name --name "serviceA-[0-9]+"
    INFO:AwsGetInstance:Instance 'i-00epg17383ba1e1cg' runs container 'ecs-default-serviceA-1-default-serviceA-b4cedd8899a7cba90b00'
    # Result:
    i-00epg17383ba1e1cg
  • Get the instance for a service by its ECS task definition name: by-task-name:
    • --service is used to search for the project's service in the configuration file.
    • By default --service is also used as the running AWS ECS task to search for.
    • It is possible to additionally add the --name option to by-task-name, which allows regular expressions. --name is preferred over the value of --service when it comes to searching for the running AWS ECS task (see Usage).
      • Use case: See Use case above for by-service-name.
    # aws_ecs_services --project <configured_project> --service <configured_service> by-task-name
    aws_ecs_services --project projectA --service serviceA by-task-name
    INFO:AwsGetInstance:Instance 'i-04ef6e335a618932a' runs task 'arn:aws:ecs:eu-west-2:<account_id>:task-definition/serviceA1:262'.
    # Result:
    i-04ef6e335a618932a
    # The same can be achieved without the use of a configuration file:
    # aws_ecs_services by-task-name --region eu-west-2 --cluster default --name serviceA

    # aws_ecs_services --project <configured_project> --service <configured_service> by-task-name --name <part_of_task_name_even_regex>
    aws_ecs_services --project projectA --service serviceA by-task-name --name "serviceA-[0-9]+"
    INFO:AwsGetInstance:Instance 'i-00epg17383ba1e1cg' runs task 'arn:aws:ecs:eu-west-2:<account_id>:task-definition/serviceA:26'.
    # Result:
    i-00epg17383ba1e1cg
  • List clusters:
    • You can list clusters like this.
    aws_ecs_services list-clusters
    # Result is a list of AWS ECS clusters. Something like:
    arn:aws:ecs:eu-west-2:<account_id>:cluster/default
    arn:aws:ecs:eu-west-2:<account_id>:cluster/default-serviceB
    arn:aws:ecs:eu-west-2:<account_id>:cluster/default-serviceC
    arn:aws:ecs:eu-west-2:<account_id>:cluster/projectB
  • In case the ecs-agent is not connected (for example), list all the EC2 instances (instance id, private IP address, Name tag):
    • You can list EC2 instances like this.
    aws_ecs_services list-ec2-instances | jq
    # Result is a list of AWS EC2 instances. Something like:
    {
      "i-07ba28172h8s17c44c": {
        "instance_type": "t3.small",
        "private_ip_address": "10.16.35.164",
        "tags": {
          "name": "projectA"
        }
      },
      "i-0rba289056hsdohe8r": {
        "instance_type": "t3.small",
        "private_ip_address": "10.16.35.154",
        "tags": {
          "name": "projectA-serviceB"
        }
      },
      "i-0d0b194d33wer5ce14": {
        "instance_type": "t3.small",
        "private_ip_address": "10.16.35.144",
        "tags": {
          "name": "projectB"
        }
      }
    }

Variable replacement

In the configuraiton file it is possible to define values for:

  • cluster (AWS ECS cluster name)
  • dns (AWS Route53 DNS name)

As you can see in ./config.template it's possible to hardcode them, That means it would be necessary to set e.g. dns for each and every service.

Making use of variable replacement really is depending on your infrastructure setup and naming schemes.

aws_ecs_services makes it possible to reuse some variables.

  • The value of the project-level "cluster" configuration is used to replace occurrences of {cluster}.
  • The value of the cli option --service is used to replace occurrences of {service}.

On the project-level, the following variable replacement is possible:

configuration (JSON key) variable replacement
"cluster" {service}
"dns" {cluster}, {service}

Note:

  • It's not possible to replace the variable {cluster} in "cluster" on project-level, because this is the value that is used to replace {cluster}. It would end up replacing itself.

On the service-level, the following variable replacement is possible:

configuration (JSON key) variable replacement
"cluster" {cluster}, {service}
"dns" {cluster}, {service}
"name" {cluster}, {service}

Note:

  • It's possible to replace the variable {cluster} in "cluster" on service-level, because in this case the project-level value for "cluster" is used to replace {cluster} on service-level.

Examples - Assume the configuration from ./config.template:

    # aws_ecs_services  --project <configured_project> --service <configured_service> by-service-dns --output id
    aws_ecs_services  --project projectA --service serviceD by-service-dns --output id
    # Raw configuration:
    {
        "region": "eu-west-1",
        "projects": {
            "projectA": {
                "region": "eu-west-2",
                "cluster": "default",
                "dns": "{service}.domain.com",
                "services": {
                    "serviceD": {
                        "cluster": "{cluster}-serviceC",
                        "dns": "serviceC.domain.com"
                    }
                }
            },
            ...
        }
    }
    # Loaded/Actual configuration:
    -> service = "serviceD"
    At first it loads:
    "region" = "eu-west-1"
    However, the final value is:
    -> "region" = "eu-west-2"
    At first it loads:
    "cluster" = "default"
    However, the final value is:
    -> "cluster" = "default-serviceC"
    At first it loads:
    "dns" = "servcieD.domain.com"
    However, the final value is:
    -> "dns" = "serviceC.domain.com"
    # Result:
    i-00epg17383ba1e1cg

requirements.txt vs. setup.py

According to these sources:

I try to stick to:

  • requirements.txt lists the necessary packages to make a deployment work.
  • setup.py declares the loosest possible dependency versions.

Creating requirements.txt

You won't ever need this probably - This is helpful when developing.

pip-tools is used to create requirements.txt.

  • There is requirements.in where dependencies are set and pinned.
  • To create the requirements.txt, run update_requirements.sh which basically just calls pip-compile.

Note:

  • There also is build_requirements.txt which only contains pip-tools. I found, when working with virtual environments, it is necessary to install pip-tools inside the virtual environment as well. Otherwise pip-sync would install outside the virtual environment.

A development environment can be created like this:

    # Create a virtual environment 'venv'.
    python -m venv venv
    # Activate the virtual environment 'venv'.
    . /venv/bin/activate
    # Install 'pip-tools'.
    pip install --upgrade -r build_requirements.txt
    # Install dependencies.
    pip-sync requirements.txt
    ...
    aws-vault -- python -m aws_ecs_services.aws_ecs_services by-service-name --region eu-west-2 --cluster dev --name "price-redis-[a-z0-9]*$
    # or (assuming an according configuration file)
    aws-vault -- python -m aws_ecs_services.aws_ecs_services --project prices --service=price-redis by-service-name
    ...
    # Deactivate the virtual environment 'venv'.
    deactivate

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