[DOCKER] How to get inside a container running on AWS Fargate

Introduction

In the case of AWS Fargate, it is inconvenient that I can not investigate because it is not in the container that is running when there is a problem, so I investigated how to enter the container.

• At this time (September 2020), there is no way to get inside the container with AWS Fargate's unique features.
• There is a way to install sshd in the container and a way to install ssm-agent

If you use ssm-agent, you don't have to open the SSH port and manage the public key to SSH, so I used ssm-agent.

How to install sshd in a container

1. Keep the SSH port open
2. Add the public key of the user to ssh to ~ / .ssh / authorzied_keys in the container
3. Install sshd in the container and start sshd when the container starts.

merit

• There is no charge to use the session manager because it does not use the session manager.

Demerit

• Need to open SSH port
• Need to manage the public key of the user to SSH

How to install ssm-agent in a container

1. When the container starts, create an activation with hybrid activation, register it, and start ssm-agent.
2. Use Session Manager to enter the container

merit

Since it uses a session manager, it has the following merits.

• No need to open SSH ports
• Eliminates the need to manage public keys for SSH users

Demerit

• There is no charge for using Session Manager for normal Amazon EC2, but since you register using hybrid activation, it will be treated as on-premises instance management, so there will be a usage charge.

https://docs.aws.amazon.com/ja_jp/systems-manager/latest/userguide/activations.html

Access to your Amazon EC2 instance is available at no additional charge.

Source code

https://github.com/f96q/fargate-ssm-sample

Includes Terraform to create an environment that runs on Dockerfile and AWS Fargate

Dockerfile

When using with Alpine, there is no ssm-agent package, so you need to bring it from the source, build it, and install it.

For other Linux distortions, we may provide an ssm-agent package that you can install, in which case you only need to install that package. https://docs.aws.amazon.com/ja_jp/systems-manager/latest/userguide/sysman-manual-agent-install.html

ARG GOLANG_TAG=1.14.4-alpine3.12
ARG ALPINE_TAG=3.12

# ssm agenet builder
FROM golang:$GOLANG_TAG as ssm-agent-builder

ARG SSM_AGENT_VERSION=2.3.1205.0

RUN apk add --no-cache \
         'make~=4.3-r0' \
         'git~=2.26.2-r0' \
         'gcc~=9.3.0-r2' \
         'libc-dev~=0.7.2-r3' \
         'bash~=5.0.17-r0'

RUN wget -q https://github.com/aws/amazon-ssm-agent/archive/${SSM_AGENT_VERSION}.tar.gz && \
    mkdir -p /go/src/github.com && \
    tar xzf ${SSM_AGENT_VERSION}.tar.gz && \
    mv amazon-ssm-agent-${SSM_AGENT_VERSION} /go/src/github.com/amazon-ssm-agent && \
    echo ${SSM_AGENT_VERSION} > /go/src/github.com/amazon-ssm-agent/VERSION

WORKDIR /go/src/github.com/amazon-ssm-agent

RUN gofmt -w agent && make checkstyle || ./Tools/bin/goimports -w agent && \
    make build-linux

# merge image
FROM alpine:$ALPINE_TAG

RUN apk add --no-cache \
      'jq~=1' \
      'aws-cli~=1.18.55-r0' \
      'sudo~=1.9.0-r0'

RUN adduser -D ssm-user && \
    echo "Set disable_coredump false" >> /etc/sudo.conf && \
    echo "ssm-user ALL=(ALL) NOPASSWD:ALL" > /etc/sudoers.d/ssm-agent-users && \
    mkdir -p /etc/amazon/ssm

COPY --from=ssm-agent-builder /go/src/github.com/amazon-ssm-agent/bin/linux_amd64/ /usr/bin
COPY --from=ssm-agent-builder /go/src/github.com/amazon-ssm-agent/bin/amazon-ssm-agent.json.template /etc/amazon/ssm/amazon-ssm-agent.json
COPY --from=ssm-agent-builder /go/src/github.com/amazon-ssm-agent/bin/seelog_unix.xml /etc/amazon/ssm/seelog.xml

COPY docker-entrypoint.sh /
ENTRYPOINT ["/docker-entrypoint.sh"]

CMD ["amazon-ssm-agent"]

docker-entrypoint.sh

#!/bin/sh

set -e


AWS_REGION=${AWS_REGION:-}
SSM_ACTIVATION=$(aws ssm create-activation --default-instance-name "fargate-ssm" --iam-role "service-role/AmazonEC2RunCommandRoleForManagedInstances" --registration-limit 1 --region $AWS_REGION)

export SSM_ACTIVATION_CODE=$(echo $SSM_ACTIVATION | jq -r .ActivationCode)
export SSM_ACTIVATION_ID=$(echo $SSM_ACTIVATION | jq -r .ActivationId)

amazon-ssm-agent -register -code $SSM_ACTIVATION_CODE -id $SSM_ACTIVATION_ID -region $AWS_REGION

exec "$@"

What you have to do manually when you finish using

https://aws.amazon.com/jp/systems-manager/pricing/#On-Premises_Instance_Management

Do the following because you will be charged for the time you are running.

• Remove hybrid activation
• Remove the registered instance