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Monday, September 08, 2025
Why Your New External Drive is Breaking Your macOS Builds
Sunday, July 20, 2025
Reusing the same Next.js Docker image with runtime CDN assetPrefix
Recently, while investigating a production issue, I needed to deploy the production Docker image locally for debugging purposes. However, I encountered a significant architectural constraint that highlighted a fundamental deployment challenge requiring both architectural and DevOps expertise to resolve.
The Challenge: CDN Configuration
Next.js provides assetPrefix configuration to specify CDN or custom domains for static asset delivery, enabling faster content delivery through geographically distributed networks. However, this configuration presents a critical architectural constraint: it's a build-time setting that gets permanently embedded into static pages and CSS assets.
This limitation creates substantial operational challenges when reusing a Docker image:
- Multiple Environments: Different environments like QA, stage, and production use different CDN domains.
- Regional CDNs: Production environments could use different regional CDN domains.
The traditional approach would require building separate Docker images for each environment, violating the fundamental DevOps principle of "build once, deploy anywhere."
Architectural Solution: Runtime Asset Prefix Injection
Through careful analysis of Next.js's asset handling mechanisms and strategic use of text replacement techniques, I developed a solution that maintains build-time optimization while enabling runtime CDN configuration.
Configuration Architecture
The solution begins with environment-aware configuration that handles both basePath and assetPrefix dynamically:
Docker Build Strategy
During the Docker image creation process, we set placeholder values that will be replaced at runtime, along with a custom entrypoint script:
Runtime Replacement Logic
The entrypoint script performs intelligent text replacement, substituting placeholder values with environment-specific configurations at container startup:
Addressing Image Security Constraints
During implementation, I encountered an additional architectural challenge: Next.js image optimization returns cryptic 404 errors when serving images from CDN domains. Investigation into the Next.js source code revealed this is a security feature that only allows pre-approved domains for image serving.
The error message "url parameter is not allowed" provides insufficient context for troubleshooting, but the root cause is Next.js's domain whitelist mechanism. This requires configuring images.remotePatterns to explicitly allow CDN domains.
Advanced Runtime Configuration
The most sophisticated aspect of this solution involves dynamically updating the remotePatterns configuration at runtime. Since we're performing text replacements on configuration files, I leveraged Node.js's command-line execution capabilities to add intelligent remotePatterns generation for CDN domain whitelisting.
This approach ensures that:
- Security policies remain enforced through domain whitelisting
- Runtime flexibility is maintained for multi-environment deployments
- Performance optimization continues through proper CDN utilization
- Operational efficiency is achieved through single-image deployment
Key Architectural Benefits
This solution delivers several critical advantages:
- Single Image Deployment: One Docker image serves all environments, reducing build complexity and storage requirements
- Runtime Flexibility: CDN configurations adapt to deployment context without rebuild cycles
- Performance Preservation: Static page optimization remains intact while enabling dynamic asset serving
- Security Compliance: Domain whitelisting ensures controlled image processing
- Operational Simplicity: Environment-specific configurations are managed through standard environment variables
Implementation Considerations
When implementing this approach, consider these architectural factors:
- Text replacement scope: Ensure replacements target only intended configuration values
- Environment variable validation: Implement proper fallbacks for missing or invalid CDN configurations
- Security boundaries: Maintain strict domain whitelisting for image processing
- Performance monitoring: Verify that runtime replacements don't impact application startup time
Conclusion
With some architectural creativity, we can resolve platform limitations while maintaining operational best practices. By combining Next.js's build-time optimizations with runtime configuration flexibility, we achieve the ideal balance of performance and deployment efficiency.
The approach enables teams to leverage CDN benefits across multiple environments while adhering to containerization principles, ultimately delivering both technical excellence and operational simplicity. For organizations deploying Next.js applications across diverse environments, this pattern provides a production-ready solution that scales with architectural complexity while maintaining deployment consistency.
Resolving Next.js Standalone Build Docker Reachability Failure on AWS ECS Fargate
While deploying a Next.js standalone build in a Docker container on AWS ECS Fargate, I encountered a subtle but critical issue that highlights the importance of understanding platform-specific runtime behaviors.
The Problem: Silent Health Check Failures
During the deployment of our Next.js application to AWS ECS Fargate, the service consistently failed health checks despite the application appearing to function correctly. The container would start successfully, but the Target Group couldn't establish connectivity, resulting in deployment failures.
Initial Investigation
Examining the container logs revealed the root cause:
The Next.js server was binding to the container's internal hostname rather than accepting connections from external networks. This prevented the ALB health checks from reaching the application endpoint.
Root Cause Analysis
Tracing through the Next.js standalone build revealed the hostname configuration logic in server.js:
The application defaults to 0.0.0.0 (accepting all connections) when no HOSTNAME environment variable is present. My initial approach was to explicitly set HOSTNAME=0.0.0.0 in the ECS task definition.
However, this approach failed due to a critical AWS Fargate behavior: Fargate automatically sets the HOSTNAME environment variable at runtime, overriding any pre-configured values.
Evaluating Solution Approaches
Approach 1: Runtime Environment Override
While functional, this approach embeds environment variable assignments within the CMD instruction, reducing container portability and maintainability.
Approach 2: Build-Time Source Modification
Using sed during the Docker build process to directly modify the hostname assignment:
Approach 3: Systematic Source Patching (Recommended as it provides consistent behavior locally and in the cloud)
The most architecturally sound solution leverages patch-package to modify the Next.js build process itself. The hostname assignment originates from node_modules/next/dist/build/utils.js in the writeFile function that generates server.js.
By creating a systematic patch that modifies the server generation logic, we achieve:
- Consistency across environments (local development and production)
- Maintainability through version-controlled patches
- Architectural integrity by addressing the root cause rather than symptoms
Implementation Details
The patch modifies the server template generation in Next.js build to use more relevant environment variable names. This ensures consistent behavior across all deployment targets while maintaining clean separation of concerns.
Key Architectural Insights
This experience reinforces several important principles for cloud-native application deployment:
- Platform Behavior Awareness: Cloud platforms often inject runtime configurations that can override application-level settings
- Health Check Design: Container applications must be designed with load balancer connectivity patterns in mind
- Source-Level Solutions: Sometimes the most maintainable solution requires modifying the build process rather than working around runtime constraints
Conclusion
While AWS Fargate's automatic hostname assignment serves legitimate infrastructure purposes, it can create unexpected challenges for containerized applications. By understanding the platform's behavior and implementing systematic source modifications, we can create robust deployment solutions that maintain architectural integrity while meeting operational requirements.
Saturday, July 19, 2025
Access logs in Next.js production build
I frequently encounter architectural decisions that seem counterintuitive from an operational perspective. Recently, while containerizing a Next.js application, I discovered one such puzzling design choice that required a creative engineering solution.
The Problem: Silent Production Builds
During the Docker image creation process for our Next.js application, I encountered an unexpected operational blind spot: Next.js production builds generate zero access logs. This absence of fundamental observability data immediately raised concerns about our ability to monitor application behavior in production environments.
The conventional wisdom suggests deploying an nginx reverse proxy to capture access logs. However, as an architect focused on operational efficiency, introducing an additional process layer solely for logging felt architecturally unsound, particularly within containerized environments where process minimalism is a core principle.
Exploring Conventional Solutions
My initial investigation led me to application-level logging libraries such as winston and pino. While these tools excel at application logging, they operate within the application boundary and don't provide the standardized access log format that operations teams expect from web applications.
Root Cause Analysis
After extensive research into similar reported issues, I discovered the underlying cause: Vercel has intentionally omitted access logging from Next.js production builds. This architectural decision, while perhaps suitable for Vercel's managed platform, creates operational challenges for self-hosted deployments.
Deep Dive
Taking a source-code-first approach, I downloaded the Next.js repository and traced the request handling flow to its core: the async function requestListener(req, res) function. By strategically placing console.log statements within the node_modules Next.js installation, I successfully exposed the access log data we needed.
However, this manual modification approach presented obvious maintainability challenges for automated deployment pipelines.
Production-Ready Implementation
While researching sustainable patching methodologies, I discovered an excellent resource by TomUps (https://www.tomups.com/posts/log-nextjs-request-response-as-json/) that introduced patch-package, a tool designed precisely for this type of systematic source modification.
Their approach provided the foundational technique, though it captured extensive request/response metadata including headers and body content. For our operational requirements, I needed a more focused solution that provided essential access log fields: timestamp, URL, and HTTP status code.
Architectural Solution
The final implementation leverages patch-package combined with pino-http-print to deliver clean, standardized access logs that integrate seamlessly with our existing observability stack. This approach:
- container efficiency by avoiding additional processes
- Provides operational visibility through standard access log formats
- Ensures deployment consistency via automated patching during image builds
- Preserves maintainability through version-controlled patch files
Key Takeaway
This experience reinforces a fundamental architectural principle: when platform decisions conflict with operational requirements, creative engineering solutions can bridge the gap while maintaining system integrity. The key is balancing pragmatic problem-solving with long-term maintainability, exactly what patch-package enables in this scenario.
Steps
You can follow the steps in TomUps post and use the following patch.
Thursday, May 22, 2025
Segmentation fault when running pip inside docker buildx on host=arm platform=amd64
Initial Troubleshooting Efforts
Root Cause Analysis
Resolution
Conclusion
NOTE
To utilize this builder, run the following command:
Monday, May 19, 2025
Multi-platform multi-stage build docker images with platform specific files
While working on multi platform docker images for a FastAPI application with MySQL client libraries, ran into a scenario where the MySQL library files are stored in platform specific paths.
As part of multi-stage build, I wanted to do something like
FROM python:${PYTHON_VERSION}-slim
# if x64
COPY --from=builder /usr/lib/x86_64-linux-gnu/libmysql* /usr/lib/x86_64-linux-gnu
# if arm
COPY --from=builder /usr/lib/aarch64-linux-gnu/libmysql* /usr/lib/aarch64-linux-gnu
But there is no conditional platform support at the COPY command level. It is only at the FROM level.
The simple solution would be to have duplicate final image setup.
COPY --from=builder /usr/lib/x86_64-linux-gnu/libmysql* /usr/lib/x86_64-linux-gnu
...
FROM --platform=arm64 python:${PYTHON_VERSION}-slim
COPY --from=builder /usr/lib/aarch64-linux-gnu/libmysql* /usr/lib/aarch64-linux-gnu
...
But this would mean duplicating rest of the steps too.
The solution is to create multiple platform specific intermediate images and use them to create the final image.
COPY --from=builder /usr/lib/x86_64-linux-gnu/libmysql* /usr/lib/x86_64-linux-gnu
COPY --from=builder /usr/lib/x86_64-linux-gnu/libmaria* /usr/lib/x86_64-linux-gnu
COPY --from=builder /usr/lib/x86_64-linux-gnu/*xslt* /usr/lib/x86_64-linux-gnu
COPY --from=builder /usr/lib/x86_64-linux-gnu/*xml* /usr/lib/x86_64-linux-gnu
FROM --platform=arm64 python:${PYTHON_VERSION}-slim as final-intermediate-arm64
COPY --from=builder /usr/lib/aarch64-linux-gnu/libmysql* /usr/lib/aarch64-linux-gnu
COPY --from=builder /usr/lib/aarch64-linux-gnu/libmaria* /usr/lib/aarch64-linux-gnu
COPY --from=builder /usr/lib/aarch64-linux-gnu/*xslt* /usr/lib/aarch64-linux-gnu
COPY --from=builder /usr/lib/aarch64-linux-gnu/*xml* /usr/lib/aarch64-linux-gnu
FROM final-intermediate-${TARGETARCH}
COPY . /code/
COPY requirements.txt /code/requirements.txt
COPY --from=builder /code/.venv /code/.venv
COPY --from=builder /usr/bin/mysql_config /usr/bin
WORKDIR /code
EXPOSE 8000
CMD ["/code/.venv/bin/uvicorn", "--app-dir", "/code/myapp", "server:app", "--proxy-headers"]
Monday, May 13, 2024
FastAPI middleware performance
As per the FastAPI docs, the way to create and add custom middlewares is
Seems simple enough. Before the await, you can do something with the request. After the await, you can do something with the response.
But if you run benchmark, you will find something very surprising.
Saturday, May 11, 2024
Python - calling async function from a sync code flow
Recently I ran into a scenario where I needed to call a init function for a third party library in my FastAPI application. The problem was, the function was async.
One way of calling an async function from a sync flow is using asyncio event loop.
But this gave event loop is already running error.
The problem is, FastAPI application is run with uvicorn which starts a loop.
So I tried creating a new loop.
But this still didn't work as asyncio only supports one loop at a time.
The most suggested approach is to use nest-asyncio.
Thursday, June 22, 2023
FastAPI and Swagger2
Requirements
Python 3.8+
FastAPI 0.79.0+
Installation
$ pip install fastapi_swagger2
Example
from typing import Union from fastapi import FastAPI from fastapi_swagger2 import FastAPISwagger2 app = FastAPI() FastAPISwagger2(app) @app.get("/") def read_root(): return {"Hello": "World"} @app.get("/items/{item_id}") def read_item(item_id: int, q: Union[str, None] = None): return {"item_id": item_id, "q": q}
This adds following endpoints:
http://localhost:8000/swagger2/docs
http://localhost:8000/swagger2/redoc
Generate spec for CI/CD
Monday, April 12, 2021
Run GUI applications inside Multipass (Ubuntu) on macOS
Multipass is a nice docker like vm platform from Ubuntu. It can configure the vm with cloud-init so you can prototype your cloud launches locally for free.
E.g. Launch an instance (by default you get the current Ubuntu LTS)
$ multipass launch --name foo
You can read more about multipass in the docs.
Primarly it does seem like just another alternative to docker. But then I found one nice little difference, not a resource hog unlike docker and you don't run as root.
Currently to run a GUI application which you just want to try without having to clean up the system, most common approach is create a vm with VirtualBox, VMware Fusion or Parallels. But it can be a time consuming task as it installs everything from scratch.
Getting GUI applications to work on docker is possible configuration. But then, atleast on Mac, Docker is a resource hog.
With multipass I was able to get IntelliJ IDEA with following:
Prerequisites:
- Install Multipass
- Install XQuartz. Also configure XAuthLocation.
echo "XAuthLocation /opt/X11/bin/xauth" >> ~/.ssh/config
Launch a vm with current LTS ubuntu with 4 cores CPU and 4 GB memory
$ multipass launch -n idea -c 4 -m 4G
$ multipass shell idea
$ sudo apt update
$ sudo apt install -y libxrender-dev libxtst6 libxi6 fontconfig
$ cd /tmp
$ curl -L -O https://download.jetbrains.com/idea/ideaIC-2021.1.tar.gz
$ sudo tar -xzf ideaIC-2021.1.tar.gz -C /opt
$ echo 'PATH=/opt/idea-IC-211.6693.111/bin:$PATH' >> ~/.bashrc
$ sudo apt install -y openjdk-11-jdk
You could automate the above with cloud-init. (Currently as of this writing multipass only supports yaml configs)
Now time for the magic part (on the host):
multipass shell internally is just doing a SSH
$ sudo cp '/var/root/Library/Application Support/multipassd/ssh-keys/id_rsa' ~/.ssh/multipass_id_rsa
Save this script to your PATH
$ cat ~/bin/multipass_x_ssh
#!/bin/bash
IP=$(multipass info $1 | grep IPv4 | awk '{ print $2 }')
ssh -X -i ~/.ssh/multipass_id_rsa ubuntu@$IP
Now when I want to run idea, all I have to do is:
$ multipass_x_ssh idea
$ idea.sh
Saturday, February 27, 2021
pyenv install error on MacOS Big Sur - sendfile invalid
There seems to be some issue going on with pyenv and MacOS Big Sur.
./Modules/posixmodule.c:8320:15: error: implicit declaration of function 'sendfile' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
ret = sendfile(in, out, offset, &sbytes, &sf, flags);
After referring multiple posts, this is what worked for me.
brew install zlib bzip2
CFLAGS="-I$(brew --prefix openssl)/include -I$(brew --prefix bzip2)/include -I$(brew --prefix readline)/include -I$(xcrun --show-sdk-path)/usr/include" LDFLAGS="-L$(brew --prefix openssl)/lib -L$(brew --prefix readline)/lib -L$(brew --prefix zlib)/lib -L$(brew --prefix bzip2)/lib" pyenv install 3.5.3 --patch < <(curl -sSL https://github.com/python/cpython/commit/8ea6353.patch\?full_index\=1)
Wednesday, February 10, 2021
Vmware Fusion 12 - Mac OS Big Sur - Could not connect Network
Was unable to get the network to work after a restart.
| vmx| I005: VNET: 'ethernet0' enable link state propagation, lsp.state = 5
| vmx| I005: DictionaryLoad: Cannot open file "/Library/Preferences/VMware Fusion/config": No such file or directory.
| vmx| I005: VNET: MACVNetMacosGetRealAdapterType: network type for adapter 0: 8
| vmx| I005: VNET: MACVNetMacosGetVnetProperties: vnet properties: vnet=vmnet8, nat=yes, dhcp=yes (ignored), subnet=172.16.82.0, mask=255.255.255.0, firstAddr=172.16.82.1, lastAddr=172.16.82.127, isIPv6=no, IPv6Prefix=fd15:4ba5:5a2b:1008::, IPv6PrefixLen=64
| vmx| I005: VNET: MACVNetPortVirtApiStartInterface: Waiting on semaphore for adapter: 0
| host-1216256| I005: VNET: MACVNetPortVirtApiStartHandler: starting interface for adapter: 0, status: 1009
| host-1216256| W003: VNET: MACVNetPortVirtApiStartHandler: unable to create virtual intrface for device: 0, status: 1009
| vmx| I005: VNET: Semaphore signalled for adapter: 0, timeoutMs=5000, waitMs=3
| vmx| W003: VNET: MACVNetPortVirtApiStartInterface: Failed to create interface for adapter: 0, handlerStatus: 1009
| vmx| I005: VNET: MACVNetPort_Connect: Ethernet0: can't start virtual interface
| vmx| I005: Msg_Post: Error
| vmx| I005: [msg.vnet.connectvnet] Could not connect 'Ethernet0' to virtual network '/dev/vmnet8'. More information can be found in the vmware.log file.
| vmx| I005: [msg.device.badconnect] Failed to connect virtual device 'Ethernet0'.
| vmx| I005: ----------------------------------------
Here's what worked for me:
- Click on "Apple" logo in menu bar
- Click "System Preferences"
- Click "Sharing"
- Disable "Internet Sharing"
- Restart the VM.
Saturday, June 20, 2020
MacOS pyenv python 3.8 tkinter install
brew install pyenv
brew install tcl-tk
echo 'export PATH="$(brew --prefix tcl-tk)/bin:$PATH"' >> ~/.zshrc
export LDFLAGS="-L$(brew --prefix tcl-tk)/lib"
export CPPFLAGS="-I$(brew --prefix tcl-tk)/include"
export PKG_CONFIG_PATH="$(brew --prefix tcl-tk)/lib/pkgconfig"
PYTHON_CONFIGURE_OPTS="--with-tcltk-includes='-I$(brew --prefix tcl-tk)/include' --with-tcltk-libs='-L$(brew --prefix tcl-tk)/lib -ltcl8.6 -ltk8.6'" CFLAGS="-I$(brew --prefix tcl-tk)/include" pyenv install 3.8.3
Monday, September 10, 2018
Duply backup on MacOS
untar
cd duplicity-0.7.18
mkvirtualenv duply_backup
brew install librsync
brew install gpg
pip install fasteners
python setup install
Download duply from https://sourceforge.net/projects/ftplicity/files/duply%20%28simple%20duplicity%29/
untar
cd duply_2.1
workon duply_backup
./duply -V
duply version 2.1
(http://duply.net)
Using installed duplicity version 0.7.18, python 2.7.14 (/Users/vkanwade/.virtualenvs/duply_backup/bin/python2), gpg 2.2.10 (Home: /Users/vkanwade/.gnupg), awk 'awk version 20070501', grep 'grep (BSD grep) 2.5.1-FreeBSD', bash '3.2.57(1)-release (x86_64-apple-darwin17)'.
export DUPL_PYTHON_BIN=~/.virtualenvs/duply_backup/bin/python
export PATH="$PATH:/opt/duply_2.1/"
duply myprofile create
vim ~/.duply/myprofile/conf
#GPG_KEY='_KEY_ID_'
GPG_PW='<some random pwd generated with pwgen. store it safe, required for restore>'
TARGET='s3://< s3_prefix>< s3_region >.amazonaws.com/< s3_bucket >/duply/myprofile'
# s3_prefix: eu-central-1 's3.', else 's3-'
export AWS_ACCESS_KEY_ID='< aws_s3_backup_id >'
export AWS_SECRET_ACCESS_KEY='< aws_s3_backup_secret >'
DUPL_PARAMS="$DUPL_PARAMS --allow-source-mismatch --s3-use-new-style --s3-european-buckets "
SOURCE='/'
MAX_AGE=1M
MAX_FULLBKP_AGE=1M
DUPL_PARAMS="$DUPL_PARAMS --full-if-older-than $MAX_FULLBKP_AGE "
ARCH_DIR=~/duply-cache
NOTE: just wanted to dump the info. formatting will come.
Tuesday, October 25, 2016
MacOS - Operation not permitted - Can't upgrade package 'six'
sudo -H pip install --upgrade python-dateutil --ignore-installed six
Saturday, October 22, 2016
Tuesday, September 22, 2015
Bash - Get output after matching line
$ cat file.txt
line 1
line 2
this is the line
line 4
line 5
If you want lines starting from "this is the line"
$ cat file.txt | awk '/this is the line/{ f=1; } f'
this is the line
line 4
line 5
When the line is found, set f to 1.
The last 'f' is shortcut to 'f == 1 { print }'
If you want output after the matching line
$ cat file.txt | awk '/this is the line/{ f=1; next; } f'
line 4
line 5
Saturday, August 01, 2015
Get celery init.d scripts
Also accepts APP_NAME as an argument. Saves the files as celeryd-<app_name> and celerybeat-<app_name>
Install Redis inside virtualenv
Puts the redis.conf in ${VIRTUAL_ENV}/etc/redis.conf.
Adds a wrapper redis-server-ve to use this conf by default.
Defaults to stable release. Else pass the version as an argument.
Monday, October 27, 2014
Packer vmware-iso on Ubuntu 14.04 with VMware Player 6
Download VMware Player 6 from:
https://my.vmware.com/web/vmware/free#desktop_end_user_computing/vmware_player/6_0|PLAYER-603|product_downloads
Also, click on Driver & Tools and download the correct version of VIX.
e.g.
$ wget https://download3.vmware.com/software/player/file/VMware-Player-6.0.3-1895310.x86_64.bundle $ chmod +x VMware-Player-6.0.3-1895310.x86_64.bundle $ sudo ./VMware-Player-6.0.3-1895310.x86_64.bundle $ wget https://download3.vmware.com/software/player/file/VMware-VIX-1.13.3-1895310.x86_64.bundle $ chmod +x VMware-VIX-1.13.3-1895310.x86_64.bundle $ sudo ./VMware-VIX-1.13.3-1895310.x86_64.bundle $ sudo apt-get install qemu-utils $ packer build vmware.json
If you see errors like vmware or vmrun not in $PATH, VIX was not installed properly.
If you see errors like "specified version not found", incorrect version of VIX was installed.
If you see qemu related errors, qemu-utils was not installed.
vmware-iso only outputs the vmware instance as .vmx along with other files.
To export to ovf/ova format
$ ovftool appliance.vmx appliance.ovf $ ovftool appliance.vmx appliance.ova
Why Your New External Drive is Breaking Your macOS Builds
Picture this: you're running dangerously low on disk space, so you invest in a brand new external drive. Time to migrate your developmen...
-
VMware Fusion provides a nice functionality of sharing folder from host (Mac OSX) to guest (Ubuntu). But then, it seems they are more focus...
-
Recently, while investigating a production issue, I needed to deploy the production Docker image locally for debugging purposes. However, I ...
-
Picture this: you're running dangerously low on disk space, so you invest in a brand new external drive. Time to migrate your developmen...