Sunday, 17 February 2019

How to Install docker on raspbian stretch

As part of one of my recent experiments I wanted to install docker on my raspberry pi. The procedure nowadays seems significantly better than a couple of years ago when I first tried. However, there are always some little details that can be a bit frustrating when following steps.

Although the process to install docker is well described in their website, it's focused on Debian distribution. We all know that Raspbian is based on Debian and therefore most of the instructions for will apply without much trouble.

That said, I will detail the exact steps I followed to get docker installed on my raspberry pi, this procedure was tested on 3B, Zero and Zero W.

First, update the package list, if you haven't done yet after setting up your raspberry pi.

$ sudo apt-get update

Install packages to allow apt to use a repository over HTTPS.

$ sudo apt-get install \
apt-transport-https \
ca-certificates \
curl \
gnupg2 \

Add Docker’s official GPG key. Note that here the url points to raspbian directory and not to debian as per the original instructions.

curl -fsSL | sudo apt-key add -

The next step recommended didn't work for me.

sudo add-apt-repository \
   "deb [arch=armhf] \
   $(lsb_release -cs) \

It failed with an error similar to this:

Traceback (most recent call last):
File "/usr/bin/add-apt-repository", line 95, in 
  sp = SoftwareProperties(options=options)
File "/usr/lib/python3/dist-packages/softwareproperties/"
, line 109, in __init__
File "/usr/lib/python3/dist-packages/softwareproperties/"
, line 599, in reload_sourceslist
File "/usr/lib/python3/dist-packages/aptsources/", line 89, 
in get_sources (, self.codename))
aptsources.distro.NoDistroTemplateException: Error: could not find a 
distribution template for Raspbian/stretch

Instead, I tried this other way, more explicitly setting up the repository into a new docker.list sources file.

$echo "deb [arch=armhf] $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list

With the new source repository in the list, update the package list again.

$ sudo apt-get update

Now we are in a position to install docker-ce from the repository, in this particular case, I ran into an issue with the latest version, documented in github basically they suggest to go back to 18.06.1 which we can get from the command below as per official docker instructions on how to get a specific version.

$ apt-cache madison docker-ce
docker-ce | 5:18.09.0~3-0~raspbian-stretch | stretch/stable armhf Packages
docker-ce | 18.06.2~ce~3-0~raspbian | stretch/stable armhf Packages
docker-ce | 18.06.1~ce~3-0~raspbian | stretch/stable armhf Packages
docker-ce | 18.06.0~ce~3-0~raspbian | stretch/stable armhf Packages

As of this writing, the version I tried is 18.06.2~ce~3-0~raspbian, which can be installed using the apt-get command.

$ sudo apt-get install docker-ce=18.06.2~ce~3-0~raspbian

Also notice that by using this vesion, there's no need to install docker-ce-cli.

Testing everything is running as expected.

$ sudo docker info
Containers: 0
 Running: 0
 Paused: 0
 Stopped: 0
Images: 1
Server Version: 18.06.2-ce
 --- more data --- 

Run the hello world. Usually we get the command sudo docker run hello-world but that only works on "normal" architectures, in this case, we're using ARMv6/7, but to make it more compatible with all of them, I ran the image from arm32v5/hello-world.

$ sudo docker run arm32v5/hello-world
Unable to find image 'arm32v5/hello-world:latest' locally
latest: Pulling from arm32v5/hello-world
590e13f69e4a: Pull complete 
Digest: sha256:8a6a26a494c03e91381161abe924a39a2ff72de13189edcc2ed1695e6be12a5f
Status: Downloaded newer image for arm32v5/hello-world:latest

Hello from Docker!
This message shows that your installation appears to be working correctly.

To generate this message, Docker took the following steps:
 1. The Docker client contacted the Docker daemon.
 2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
 3. The Docker daemon created a new container from that image which runs the
    executable that produces the output you are currently reading.
 4. The Docker daemon streamed that output to the Docker client, which sent it
    to your terminal.

To try something more ambitious, you can run an Ubuntu container with:
 $ docker run -it ubuntu bash

Share images, automate workflows, and more with a free Docker ID:

For more examples and ideas, visit:

And that's all, docker installed up and running on a raspberry pi.


If you'd like to get rid of the sudo command every time you use docker, then you can run the following command found in the official guide as a post-installation step. You don't need to create the group as it's already created by docker installation. It adds your user to the docker group.

$ sudo usermod -aG docker $USER

You need to log out and back in for this change to take effect. After that you'll be able to run all docker commands as a regular user.

Thursday, 7 February 2019

Querying Aurora serverless database remotely using Lambda - part 3

This post is part of a series

In the previous part, we've set up the Aurora MySql cluster. At this point we can start creating the client code to allow querying.

The Lambda code

In this example I'll be using .NET Core 2.1 as Lambda runtime and C# as programming language. The code is very simple and should be easy to port to your favourite runtime/language.

Lambda Input

The input to my function consists of two main pieces of information: database connection information and the query to execute.

    public class ConnectionInfo
        public string DbUser { get; set; }
        public string DbPassword { get; set; }
        public string DbName { get; set; }
        public string DbHost { get; set; }
        public int DbPort { get; set; }

    public class LambdaInput
        public ConnectionInfo Connection { get; set; }

        public string QueryText { get; set; }

Lambda Code

The function itself returns a List of dictionary where each item of the list represents a "record" from the query result, these are in a key/value form where key is the "field" name and the value is the what comes form the query.

    public List<Dictionary<string, object>> RunQueryHandler(LambdaInput input, ILambdaContext context)
        var cxnString = GetCxnString(input.Connection);
        var query = input.QueryText;

        var result = new List<Dictionary<string, object>>();
        using (var conn = new MySql.Data.MySqlClient.MySqlConnection(cxnString))
            var cmd = GetCommand(conn, query);
            var reader = cmd.ExecuteReader();

            var columns = new List<string>();

            for (int i = 0; i < reader.FieldCount; i++)

            while (reader.Read())
                var record = new Dictionary<string, object>();
                foreach (var column in columns)
                    record.Add(column, reader[column]);
        return result;

Support methods

Here is the code of the missing methods: GetCxnString and GetCommand not really complicated.

    private static readonly string cxnStringFormat = "server={0};uid={1};pwd={2};database={3};Connection Timeout=60";

    private string GetCxnString(ConnectionInfo cxn)
        return string.Format(cxnStringFormat, cxn.DbHost, cxn.DbUser, cxn.DbPassword, cxn.DbName);

    private static MySqlCommand GetCommand(MySqlConnection conn, string query)
        var cmd = conn.CreateCommand();
        cmd.CommandText = query;
        cmd.CommandType = CommandType.Text;
        return cmd;

Project file

Before compiling and packaging the code we need a project file, assuming you don't have one already, this is how it looks like to be able to run in AWS Lambda environment.

<Project Sdk="Microsoft.NET.Sdk">


    <PackageReference Include="Amazon.Lambda.Core" Version="1.0.0" />
    <PackageReference Include="Amazon.Lambda.Serialization.Json" Version="1.3.0" />
    <PackageReference Include="MySql.Data" Version="8.0.13" />
    <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />

    <DotNetCliToolReference Include="Amazon.Lambda.Tools" Version="2.2.0" />

Preparing Lambda package

Assuming you have both the code and csproj file in the current directory, we just run dotnet lambda package command as per below, where -c sets the Configuration to release, -f sets the target framework to netcoreapp2.1 and -o sets the output zip file name.

$ dotnet lambda package -c release -f netcoreapp2.1 -o
Amazon Lambda Tools for .NET Core applications (2.2.0)
Project Home:,

Executing publish command
Deleted previous publish folder
... invoking 'dotnet publish', working folder '/home/abel/Downloads/aurora_cluster_sample/bin/release/netcoreapp2.1/publish'

( ... ) --- removed code for brevity ---

... zipping:   adding: aurora.lambda.deps.json (deflated 76%)
Created publish archive (/home/abel/Downloads/aurora_cluster_sample/
Lambda project successfully packaged: /home/abel/Downloads/aurora_cluster_sample/

Next, we upload the resulting zip file to an S3 bucket of our choice. In this example I'm using a bucket named abelperez-temp and I'm uploading the zip file to a folder named aurora-lambda so I keep some form of organisation in my file directory.

$ aws s3 cp s3://abelperez-temp/aurora-lambda/
upload: ./ to s3://abelperez-temp/aurora-lambda/

Lambda stack

To create the Lambda function, I've put together a CloudFormation template that includes:

  • AWS::EC2::SecurityGroup contains outbound traffic rule to allow port 3306
  • AWS::IAM::Role contains an IAM role to allow the Lambda function to write to CloudWatch Logs and interact with ENIs
  • AWS::Lambda::Function contains the function definition

Here is the full template, the required parameters are VpcId, SubnetIds and LambdaS3Bucket which we should get from previous stacks' outputs. The template outputs the function full name, which we'll need to be able to invoke it later.

Special attention to the Lambda function definition, the property Handler, in .NET runtime is in the form of AssemblyName::Namespace.ClassName::MethodName and the property Code containing the S3 location of the zip file we uploaded earlier.

Description: Template to create a lambda function 

    Type: String
    Type: Number
    Default: 3306
    Type: String
    Type: CommaDelimitedList

    Type: AWS::EC2::SecurityGroup
      GroupDescription: Allow outbound traffic to MySQL host
        Ref: VpcId
        - IpProtocol: tcp
          FromPort: !Ref DbClusterPort
          ToPort: !Ref DbClusterPort

    Type: AWS::IAM::Role
        Version: 2012-10-17
          - Effect: Allow
            Action: sts:AssumeRole
      Path: /
        - PolicyName: PermitLambda
            Version: 2012-10-17
            - Effect: Allow
              - logs:CreateLogGroup
              - logs:CreateLogStream
              - logs:PutLogEvents
              - ec2:CreateNetworkInterface
              - ec2:DescribeNetworkInterfaces
              - ec2:DeleteNetworkInterface
                - "arn:aws:logs:*:*:*"
                - "*"
    Type: AWS::Lambda::Function
      Handler: aurora.lambda::project.lambda.Function::RunQueryHandler
      Role: !GetAtt AWSLambdaExecutionRole.Arn
        S3Bucket: !Ref LambdaS3Bucket
        S3Key: aurora-lambda/
      Runtime: dotnetcore2.1
      Timeout: 30
          - !Ref LambdaSg
        SubnetIds: !Ref SubnetIds

    Value: !Ref HelloLambda

To deploy this stack we use the following command where we pass the parameters specific to our VPC (VpcId and SubnetIds) as well as the S3 bucket name.

$ aws cloudformation deploy --stack-name fn-stack \
--template-file aurora_lambda_template.yml \
--parameter-overrides VpcId=vpc-0b442e5d98841996c SubnetIds=subnet-013d0bbb3eca284a2,subnet-00c67cfed3ab0a791 LambdaS3Bucket=abelperez-temp \
--capabilities CAPABILITY_IAM

Waiting for changeset to be created..
Waiting for stack create/update to complete
Successfully created/updated stack - fn-stack

Let's get the outputs as we'll need this information later. We have the Lambda function full name.

$ aws cloudformation describe-stacks --stack-name fn-stack --query Stacks[*].Outputs
            "OutputKey": "LambdaFunction",
            "OutputValue": "fn-stack-HelloLambda-C32KDMYICP5W"

Invoking Lambda function

Now that we have deployed the function and we know its full name, we can invoke it by using dotnet lambda invoke-function command. Part of this job is to prepare the payload which is a JSON in put corresponding to the Lambda input defined above.

    "Connection": {
        "DbUser": "master", 
        "DbPassword": "Aurora.2019", 
        "DbName": "dbtest", 
        "DbHost": "", 
        "DbPort": 3306
    "QueryText":"show databases;"

Here is the command to invoke the Lambda function, including the payload parameter encoded to escape the quotes and all in a single line. There are better ways to do this, but for the sake of this demonstration, it's good enough.

$ dotnet lambda invoke-function \
--function-name fn-stack-HelloLambda-C32KDMYICP5W \
--payload "{ \"Connection\": {\"DbUser\": \"master\", \"DbPassword\": \"Aurora.2019\", \"DbName\": \"dbtest\", \"DbHost\": \"\", \"DbPort\": 3306}, \"QueryText\":\"show databases;\" }" \
--region eu-west-1

Amazon Lambda Tools for .NET Core applications (2.2.0)
Project Home:,


Log Tail:
START RequestId: 595944b5-73bb-4536-be92-a42652125ba8 Version: $LATEST
END RequestId: 595944b5-73bb-4536-be92-a42652125ba8
REPORT RequestId: 595944b5-73bb-4536-be92-a42652125ba8  Duration: 11188.62 ms   Billed Duration: 11200 ms       Memory Size: 128 MB     Max Memory Used: 37 MB

Now we can see the output in the Payload section. And that's how we can query remotely any Aurora serverless cluster without having to set up any EC2 instance. This could be extended to handle different SQL operations such as Create, Insert, Delete, etc.

Monday, 4 February 2019

Querying Aurora serverless database remotely using Lambda - part 2

This post is part of a series

In the previous part, we've set up the base layer to deploy our resources. At this point we can create the database cluster.

Aurora DB Cluster

Assuming we have our VPC ready with at least two subnets to comply with high availability best practices, let's create our cluster, I've put together a CloudFormation template that includes:

  • AWS::EC2::SecurityGroup contains inbound traffic rule to allow port 3306
  • AWS::RDS::DBSubnetGroup contains a group of subnets to deploy the cluster
  • AWS::EC2::DBCluster contains all the parameters to create the database cluster

Here is the full template, the only required parameters are VpcId and SubnetIds, but feel free to override any of the database cluster parameters such as database name, user name, password, etc. The template outputs the IDs corresponding to newly created resources such as the database cluster DNS endpoint, port and the security group.

Description: Template to create a serverless aurora mysql cluster

    Type: String
    Default: dbtest
    Type: String
    Default: serverless-mysql-aurora
    Type: String
    Default: default.aurora5.6
    Type: String
    Default: master
    Type: String
    Default: Aurora.2019
    Type: Number
    Default: 3306
    Type: String
    Type: CommaDelimitedList

    Type: AWS::EC2::SecurityGroup
      GroupDescription: Allow MySQL port to client host
        Ref: VpcId
        - IpProtocol: tcp
          FromPort: !Ref DbClusterPort
          ToPort: !Ref DbClusterPort

    Type: "AWS::RDS::DBSubnetGroup"
      DBSubnetGroupDescription: "aurora subnets"
      SubnetIds: !Ref SubnetIds

    Type: AWS::RDS::DBCluster
        Ref: DbClusterDatabaseName
        Ref: DbClusterParameterGroup
        Ref: DbSubnetGroup
      Engine: aurora
      EngineMode: serverless
        Ref: DbClusterMasterUsername
        Ref: DbClusterMasterPassword
        AutoPause: true
        MinCapacity: 2
        MaxCapacity: 4
        SecondsUntilAutoPause: 1800
        - !Ref DbClusterSg
    Value: !GetAtt AuroraMysqlCluster.Endpoint.Address
    Value: !GetAtt AuroraMysqlCluster.Endpoint.Port
    Value: !Ref DbClusterSg

To deploy this stack we use the following command where we pass the parameters specific to our VPC (VpcId and SubnetIds).

$ aws cloudformation deploy --stack-name db-stack \
--template-file aurora_cluster_template.yml \
--parameter-overrides VpcId=vpc-0b442e5d98841996c SubnetIds=subnet-013d0bbb3eca284a2,subnet-00c67cfed3ab0a791

Waiting for changeset to be created..
Waiting for stack create/update to complete
Successfully created/updated stack - db-stack

Let's get the outputs as we'll need this information later. We have the cluster endpoint DNS name and the port as per our definition.

$ aws cloudformation describe-stacks --stack-name db-stack --query Stacks[*].Outputs
            "OutputKey": "DbClusterEndpointAddress",
            "OutputValue": ""
            "OutputKey": "DbClusterSgId",
            "OutputValue": "sg-072bbf2078caa0f46"
            "OutputKey": "DbClusterEndpointPort",
            "OutputValue": "3306"

In the next part, we'll create the Lambda function to query this database remotely.