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Dockerizing a Foundry project

This tutorial shows you how to build, test, and deploy a smart contract using Foundry's Docker image. It adapts code from the solmate nft tutorial. If you haven't completed that tutorial yet, and are new to solidity, you may want to start with it first. Alternatively, if you have some familiarity with Docker and Solidity, you can use your own existing project and adjust accordingly. The full source code for both the NFT and the Docker stuff is available here.

This tutorial is for illustrative purposes only and provided on an as-is basis. The tutorial is not audited nor fully tested. No code in this tutorial should be used in a production environment.

Installation and Setup

The only installation required to run this tutorial is Docker, and optionally, an IDE of your choice. Follow the Docker installation instructions.

To keep future commands succinct, let's re-tag the image:
docker tag ghcr.io/foundry-rs/foundry:latest foundry:latest

Having Foundry installed locally is not strictly required, but it may be helpful for debugging. You can install it using foundryup.

Finally, to use any of the cast or forge create portions of this tutorial, you will need access to an Ethereum node. If you don't have your own node running (likely), you can use a 3rd party node service. We won't recommend a specific provider in this tutorial. A good place to start learning about Nodes-as-a-Service is Ethereum's article on the subject.

For the rest of this tutorial, it is assumed that the RPC endpoint of your ethereum node is set like this: export RPC_URL=<YOUR_RPC_URL>

A tour around the Foundry docker image

The docker image can be used in two primary ways:

  1. As an interface directly to forge and cast
  2. As a base image for building your own containerized test, build, and deployment tooling

We will cover both, but let's start by taking a look at interfacing with foundry using docker. This is also a good test that your local installation worked!

We can run any of the cast commands against our docker image. Let's fetch the latest block information:

$ docker run foundry "cast block --rpc-url $RPC_URL latest"
baseFeePerGas        "0xb634241e3"
difficulty           "0x2e482bdf51572b"
extraData            "0x486976656f6e20686b"
gasLimit             "0x1c9c380"
gasUsed              "0x652993"
hash                 "0x181748772da2f968bcc91940c8523bb6218a7d57669ded06648c9a9fb6839db5"
logsBloom            "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"
miner                "0x1ad91ee08f21be3de0ba2ba6918e714da6b45836"
mixHash              "0xb920857687476c1bcb21557c5f6196762a46038924c5f82dc66300347a1cfc01"
nonce                "0x1ce6929033fbba90"
number               "0xdd3309"
parentHash           "0x39c6e1aa997d18a655c6317131589fd327ae814ef84e784f5eb1ab54b9941212"
receiptsRoot         "0x4724f3b270dcc970f141e493d8dc46aeba6fffe57688210051580ac960fe0037"
sealFields           []
sha3Uncles           "0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347"
size                 "0x1d6bb"
stateRoot            "0x0d4b714990132cf0f21801e2931b78454b26aad706fc6dc16b64e04f0c14737a"
timestamp            "0x6246259b"
totalDifficulty      "0x9923da68627095fd2e7"
transactions         [...]
uncles               []

If we're in a directory with some Solidity source code, we can mount that directory into docker and use forge however we wish. For example:

$ docker run -v $PWD:/app foundry "forge test --root /app --watch"
{{#include ../output/nft_tutorial/forge-test:output}}

You can see our code was compiled and tested entirely within the container. Also, since we passed the --watch option, the container will recompile the code whenever a change is detected.

Note: The Foundry docker image is built on alpine and designed to be as slim as possible. For this reason, it does not currently include development resources like git. If you are planning to manage your entire development lifecycle within the container, you should build a custom development image on top of Foundry's image.

Creating a "build and test" image

Let's use the Foundry docker image as a base for using our own Docker image. We'll use the image to:

  1. Build our solidity code
  2. Run our solidity tests

A simple Dockerfile can accomplish these two goals:

# Use the latest foundry image
FROM ghcr.io/foundry-rs/foundry

# Copy our source code into the container
WORKDIR /app

# Build and test the source code
COPY . .
RUN forge build
RUN forge test

You can build this docker image and watch forge build/run the tests within the container:

$ docker build --no-cache --progress=plain .

Now, what happens if one of our tests fails? Modify src/test/NFT.t.sol as you please to make one of the tests fails. Try to build image again.

$ docker build --no-cache --progress=plain .
<...>
#9 0.522 Failed tests:
#9 0.522 [FAIL. Reason: Ownable: caller is not the owner] testWithdrawalFailsAsNotOwner() (gas: 193917)
#9 0.522
#9 0.522 Encountered a total of 1 failing tests, 9 tests succeeded
------
error: failed to solve: executor failed running [/bin/sh -c forge test]: exit code: 1

Our image failed to build because our tests failed! This is actually a nice property, because it means if we have a Docker image that successfully built (and therefore is available for use), we know the code inside the image passed the tests.*

*Of course, chain of custody of your docker images is very important. Docker layer hashes can be very useful for verification. In a production environment, consider signing your docker images.

Creating a deployer image

Now, we'll move on to a bit more of an advanced Dockerfile. Let's add an entrypoint that allows us to deploy our code by using the built (and tested!) image. We can target the Rinkeby testnet first.

# Use the latest foundry image
FROM ghcr.io/foundry-rs/foundry

# Copy our source code into the container
WORKDIR /app

# Build and test the source code
COPY . .
RUN forge build
RUN forge test

# Set the entrypoint to the forge deployment command
ENTRYPOINT ["forge", "create"]

Let's build the image, this time giving it a name:

$ docker build --no-cache --progress=plain -t nft-deployer .

Here's how we can use our docker image to deploy:

$ docker run nft-deployer --rpc-url $RPC_URL --constructor-args "ForgeNFT" "FNFT" "https://ethereum.org" --private-key $PRIVATE_KEY ./src/NFT.sol:NFT
No files changed, compilation skipped
Deployer: 0x496e09fcb240c33b8fda3b4b74d81697c03b6b3d
Deployed to: 0x23d465eaa80ad2e5cdb1a2345e4b54edd12560d3
Transaction hash: 0xf88c68c4a03a86b0e7ecb05cae8dea36f2896cd342a6af978cab11101c6224a9

We've just built, tested, and deployed our contract entirely within a docker container! This tutorial was intended for testnet, but you can run the exact same Docker image targeting mainnet and be confident that the same code is being deployed by the same tooling.

Why is this useful?

Docker is about portability, reproducibility, and environment invariance. This means you can be less concerned about unexpected changes when you switch between environments, networks, developers, etc. Here are a few basic examples of why I like to use Docker images for smart contract deployment:

  • Reduces overhead of ensuring system level dependencies match between deployment environments (e.g. does your production runner always have the same version of forge as your dev runner?)
  • Increases confidence that code has been tested prior to deployment and has not been altered (e.g. if, in the above image, your code re-compiles on deployment, that's a major red flag).
  • Eases pain points around segregation of duties: people with your mainnet credentials do not need to ensure they have the latest compiler, codebase, etc. It's easy to ensure that the docker deploy image someone ran in testnet is identical to the one targeting mainnet.
  • At the risk of sounding web2, Docker is an accepted standard on virtually all public cloud providers. It makes it easy to schedule jobs, tasks, etc that need to interact with the blockchain.

Troubleshooting

As noted above, the Foundry image does not include git by default. This can cause certain commands to fail without a clear cause. For example:

$ docker run foundry "forge init --no-git /test"
Initializing /test...
Installing ds-test in "/test/lib/ds-test", (url: https://github.com/dapphub/ds-test, tag: None)
Error:
   0: No such file or directory (os error 2)

Location:
   cli/src/cmd/forge/install.rs:107

In this case, the failure is still caused by a missing git installation. The recommended fix is to build off the existing Foundry image and install any additional development dependencies you need.