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fix(iam): IAM Policies are too large to deploy
The policies we generate sometimes have a lot of duplication between statements. This duplication can lead to the policy going over the size limit an IAM policy (either 2k, 6k or 10k bytes, depending on the resource type). This change combines multiple statements together, as long as it doesn't change the meaning of the final policy. Because doing so for all existing stacks will probably provoke minor heart attacks in operators everywhere, the new behavior is gated behind a feature flag. It can be retroactively switched on by people currently being bit by the size issues: ``` @aws-cdk/aws-iam:minimizePolicies ``` Fixes #18774, fixes #16350, fixes #18457.
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packages/@aws-cdk/aws-iam/lib/private/merge-statements.ts
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,176 @@ | ||
| const LENGTH_CACHE_SYM = Symbol(); | ||
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| type IamValue = unknown | unknown[]; | ||
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| /** | ||
| * Only the parts of the policy schema we're interested in | ||
| */ | ||
| interface StatementSchema { | ||
| readonly Sid?: string; | ||
| readonly Effect?: string; | ||
| readonly Principal?: IamValue | Record<string, IamValue>; | ||
| readonly Resource?: IamValue; | ||
| readonly Action?: IamValue; | ||
| } | ||
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| /** | ||
| * Merge as many statements as possible to shrink the total policy doc, modifying the input array in place | ||
| */ | ||
| export function mergeStatements(statements: StatementSchema[]): StatementSchema[] { | ||
| let merges = findMerges(statements); | ||
| while (merges.length > 0) { | ||
| merges.sort((a, b) => a.sizeDelta - b.sizeDelta); // Most negative number first | ||
| if (merges[0].sizeDelta >= 0) { break; } // Nothing more to be gained | ||
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| // Apply all merges, order biggest to smallest gain | ||
| while (merges.length > 0 && merges[0].sizeDelta < 0) { // Only while we're not adding size | ||
| const merge = merges.shift()!; | ||
| statements[merge.i0] = merge.combined; | ||
| statements.splice(merge.i1, 1); | ||
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| // This invalidates all merges involving i0 or i1, and adjusts all indices > i1 | ||
| const invalidIndices = [merge.i0, merge.i1]; | ||
| let j = 0; | ||
| while (j < merges.length) { | ||
| if (invalidIndices.includes(merges[j].i0) || invalidIndices.includes(merges[j].i1)) { | ||
| merges.splice(j, 1); | ||
| } else { | ||
| if (merges[j].i0 > merge.i1) { merges[j].i0 -= 1; } | ||
| if (merges[j].i1 > merge.i1) { merges[j].i1 -= 1; } | ||
| j++; | ||
| } | ||
| } | ||
| } | ||
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| merges = findMerges(statements); | ||
| } | ||
| return statements; | ||
| } | ||
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| function findMerges(statements: StatementSchema[]): StatementMerge[] { | ||
| const ret = new Array<StatementMerge>(); | ||
| for (let i0 = 0; i0 < statements.length; i0++) { | ||
| for (let i1 = i0 + 1; i1 < statements.length; i1++) { | ||
| tryMerge(statements, i0, i1, ret); | ||
| } | ||
| } | ||
| return ret; | ||
| } | ||
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| function tryMerge(statements: StatementSchema[], i0: number, i1: number, into: StatementMerge[]) { | ||
| const a = statements[i0]; | ||
| const b = statements[i1]; | ||
| if (a.Effect !== 'Allow' || b.Effect !== 'Allow') { return; } | ||
| if (a.Sid || b.Sid) { return; } | ||
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| const beforeLen = jsonLength(a) + jsonLength(b); | ||
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| tryMerging('Resource'); | ||
| tryMerging('Action'); | ||
| tryMerging('Principal'); | ||
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| function tryMerging<A extends keyof StatementSchema>(key: A) { | ||
| if (!deepEqual(a, b, [key])) { return; } | ||
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| const combined = { | ||
| ...a, | ||
| [key]: mergeValues(a[key], b[key]), | ||
| }; | ||
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| into.push({ | ||
| i0, | ||
| i1, | ||
| combined, | ||
| sizeDelta: jsonLength(combined) - beforeLen, | ||
| }); | ||
| } | ||
| } | ||
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| /** | ||
| * Return the length of a JSON representation of the given object, cached on the object | ||
| */ | ||
| function jsonLength<A extends StatementSchema>(x: A): number { | ||
| if ((x as any)[LENGTH_CACHE_SYM]) { | ||
| return (x as any)[LENGTH_CACHE_SYM]; | ||
| } | ||
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| const length = JSON.stringify(x).length; | ||
| Object.defineProperty(x, LENGTH_CACHE_SYM, { | ||
| value: length, | ||
| enumerable: false, | ||
| }); | ||
| return length; | ||
| } | ||
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| function deepEqual(a: any, b: any, ignoreKeys: string[]): boolean { | ||
| // Short-circuit same object identity as well | ||
| if (a === b) { return true; } | ||
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| if (Array.isArray(a) || Array.isArray(b)) { | ||
| if (!Array.isArray(a) || !Array.isArray(b) || a.length !== b.length) { return false; } | ||
| return a.every((x, i) => deepEqual(x, b[i], [])); | ||
| } | ||
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| if (typeof a === 'object' || typeof b === 'object') { | ||
| if (typeof a !== 'object' || typeof b !== 'object') { return false; } | ||
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| const keysA = new Set(Object.keys(a)); | ||
| const keysB = new Set(Object.keys(b)); | ||
| for (const k of ignoreKeys) { | ||
| keysA.delete(k); | ||
| keysB.delete(k); | ||
| } | ||
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| for (const k of keysA) { | ||
| if (!deepEqual(a[k], b[k], [])) { return false; } | ||
| keysB.delete(k); | ||
| } | ||
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| return keysB.size === 0; | ||
| } | ||
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| return false; | ||
| } | ||
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| function mergeValues(a: IamValue, b: IamValue): any { | ||
| if (!a && !b) { return a; } | ||
| if (Array.isArray(a) && Array.isArray(b)) { return normalizedArray(...a, ...b); } | ||
| if (Array.isArray(a) && typeof b === 'string') { return normalizedArray(...a, b); } | ||
| if (Array.isArray(b) && typeof a === 'string') { return normalizedArray(a, ...b); } | ||
| if (typeof a === 'string' && typeof b === 'string') { return normalizedArray(a, b); } | ||
| if (typeof a === 'object' && typeof b === 'object' && b != null) { | ||
| const ret: any = { ...a }; | ||
| for (const [k, v] of Object.entries(b)) { | ||
| ret[k] = ret[k] ? mergeValues(ret[k], v) : v; | ||
| } | ||
| return ret; | ||
| } | ||
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| throw new Error(`Don't know how to merge ${JSON.stringify(a)} and ${JSON.stringify(b)}`); | ||
| } | ||
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| function normalizedArray(...xs: unknown[]) { | ||
| return Array.from(new Set(xs)).sort(); | ||
| } | ||
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| interface StatementMerge { | ||
| /** | ||
| * Index of statement 0 | ||
| */ | ||
| i0: number; | ||
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| /** | ||
| * Index of statement 1 | ||
| */ | ||
| i1: number; | ||
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| /** | ||
| * The result of combining them | ||
| */ | ||
| readonly combined: StatementSchema; | ||
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| /** | ||
| * How many bytes the new schema is bigger than the old one | ||
| */ | ||
| readonly sizeDelta: number; | ||
| } |
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