LOCKEDIN / FORWARD-DEPLOYED ENGINEERING 101
Understand it.
Then build it.
You can be an experienced engineer and still be new to agents. Start with what each thing is and how it helps a person do useful work. Explore 58 original introductions across software, agents, cloud, security and delivery. Start here without a model key; each topic connects to deeper instruction and practice.
A place to start.
Choose a short reading route, or look up a concept below.
- 101UnderstandPlain language, visual walkthrough, vocabulary
- 102Build with guidanceOriginal lessons, examples and knowledge checks
- 103Practise and explainRunnable labs, failure cases and handover
Connect the software
Understand how that program receives its settings and why different processes can behave differently.
See the 9-concept route
For people who want the software vocabulary behind AI tools, or a refresher before their first local build.
- 01Terminal & CLIBegin with a person issuing a command to a program; the terminal is not itself an agent.
- 02ConfigurationYou are here
- 03JSON & schemasRead the messages programs exchange. Separate a field's name, type and meaning before following an API request.
- 04APIsMove from a person using a command to one program requesting something from another.
- 05RESTSee how resource addresses, HTTP methods and status codes organize a web API.
- 06SDKsFollow the library code that turns a convenient method call into an API request.
- 07TestsDecide what observable behavior to check before trusting a change made by a person or an agent.
- 08GitSeparate editable files, selected snapshots and recorded commits. Match the tested content to the change you hand over.
- 09Claude CodeBring commands, configuration and checks into a bounded coding-assistant task.
Bookmark this page to return to this concept. The number shows your place in the reading route; it is not an assessment result.
Settings supplied to a running program
What are environment variables and configuration?
Configuration is the set of settings an application uses to choose its behavior. An environment variable is a named text value available to a running process, such as an attempt limit. A dotenv file stores settings as name=value lines. The file must be loaded by a runtime, library or framework before its values affect the program.
An FDE moves an application between a laptop, a client environment and deployment. The same code can behave differently because its launch settings differ. Trace where each effective value comes from before changing prompts or reinstalling an SDK.
UNDERSTAND THE SYSTEM
How does a setting reach the running program?
A fictional draft service needs an attempt limit and a credential before creating a client. Follow six views of a real local Node.js experiment. Credentials are represented only as present or absent; no service is contacted.
Read the connections in plain English
- 01Configuration file → Running process
--env-file loads this fixture before the program runs.
- 02Launch environment → Running process
For Node's --env-file, an inherited value wins over the same name in the file.
- 03Running process → Startup check
Read only the required names, then validate their types and allowed range.
- 04Startup check → Safe diagnostic
Presence is observable without publishing a credential value.
Check your understanding: The configuration file says 2, but the app reports 4. What evidence would you ask for?
Identify the running process, launch settings, exact loading command and loader precedence. Inspect the allowlisted effective limit and required-setting presence. Do not request a credential value or a dump of the entire environment.
CONNECT IT TO WHAT YOU KNOW
Start with something familiar.
Think of running the same test program with different input fixtures. The code can stay unchanged while the supplied settings change its behavior. Each launch receives its own inputs.
Configuration is not an ordinary request payload, and a running process does not continuously reread a file unless you build that behavior. A credential may be part of the inputs, but it must not become part of the public output.
Words worth knowing
- Process
- One running instance of a program, with its own memory and environment.
- Environment variable
- A named text value supplied to a process; it is not automatically shared with every program.
- Dotenv file
- A text file of settings. The loader decides when and how its values enter the process.
- Precedence
- The rule that chooses a value when multiple sources define the same name.
- Secret
- A sensitive value, such as a credential, that must be restricted and kept out of public code, browser output and logs.
Useful foundations
Open a definition and diagram here. Your lesson stays in place.
Interfaces to programsWhat are a terminal, a shell and a CLI?
QUICK REFERENCE / 101
What are a terminal, a shell and a CLI?
A terminal is the window where you type and see text. A shell interprets your commands. A command-line interface (CLI) is how a program accepts those commands. An AI coding agent can use a terminal, but the terminal itself does not reason or decide what to do.
You need to understand what will run, in which folder, and with whose authority before approving a coding agent's action.
ONE EXAMPLE / FICTIONAL CASE
Follow the connections.
A fictional draft service allows two attempts on a laptop but four in another launch. The file still says two. An inherited environment value overrides that file in the supplied Node.js lab; the application reports the effective limit without displaying its credential.
UNDERSTAND THE SYSTEM
How does a setting reach the running program?
A fictional draft service needs an attempt limit and a credential before creating a client. Follow six views of a real local Node.js experiment. Credentials are represented only as present or absent; no service is contacted.
See what moves and why.
Read the connections in plain English
- 01Configuration file → Running process
--env-file loads this fixture before the program runs.
- 02Launch environment → Running process
For Node's --env-file, an inherited value wins over the same name in the file.
- 03Running process → Startup check
Read only the required names, then validate their types and allowed range.
- 04Startup check → Safe diagnostic
Presence is observable without publishing a credential value.
Check your understanding: The configuration file says 2, but the app reports 4. What evidence would you ask for?
Identify the running process, launch settings, exact loading command and loader precedence. Inspect the allowlisted effective limit and required-setting presence. Do not request a credential value or a dump of the entire environment.
Work through it, step by step.
Name the setting and source
Separate ordinary settings from credentials. Identify the launcher, optional file, loader and intended process. A file name alone does not tell you whether it was loaded.
What you have now: A small map of configuration sources.
Load, convert and validate
Environment values arrive as strings. Check required fields and allowed values before creating a client. Define precedence for the loader you actually use.
What you have now: A usable configuration or a clear startup refusal.
Observe the effective configuration
Report only approved nonsecret settings and credential presence. Determine whether updates require a restart or an explicit reload mechanism.
What you have now: A safe diagnostic associated with a particular process.
FROM RECOGNITION TO REASONING
Explain six local process observations and diagnose a conflicting setting.
- 01
Predict what happens with an unloaded file, an inherited override and an invalid number.
- 02
Run the Node.js 24 lab and compare a file edit with a child-process change.
- 03
Disable the inherited override and repair the invalid value in separate copies; explain the changed evidence.
Six observations, two controlled changes and a configuration handover card with no credential values.
Compare your reasoning when you are ready
The loader supplies text and the application validates it. A file edit does not update this already-running process. An inherited setting can win on the next launch. Safe diagnostics establish presence and effective nonsecret values, not successful authentication or production readiness.
Keep notes in your own working copy. Moving through these cards does not record completion.
TURN THE IDEA INTO USEFUL WORK
You can now go deeper.
A file, a process environment and a deployed configuration are different things. Correctly loading a credential does not establish that it is valid or authorized, and an environment variable is not a secret-management system.
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